which symbol is used for variable assignment in postgresql

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PostgreSQL: Declaring Variables

This PostgreSQL tutorial explains how to declare variables in PostgreSQL with syntax and examples.

What is a variable in PostgreSQL?

In PostgreSQL, a variable allows a programmer to store data temporarily during the execution of code.

The syntax to declare a variable in PostgreSQL is:

Parameters or Arguments

Example - declaring a variable.

Below is an example of how to declare a variable in PostgreSQL called vSite .

This example would declare a variable called vSite as a varchar data type.

You can then later set or change the value of the vSite variable, as follows:

This statement would set the vSite variable to a value of 'TechOnTheNet.com'.

Example - Declaring a variable with an initial value (not a constant)

Below is an example of how to declare a variable in PostgreSQL and give it an initial value. This is different from a constant in that the variable's value can be changed later.

This would declare a variable called vSite as a varchar data type and assign an initial value of 'TechOnTheNet.com'.

You could later change the value of the vSite variable, as follows:

This SET statement would change the vSite variable from a value of 'TechOnTheNet.com' to a value of 'CheckYourMath.com'.

Example - Declaring a constant

Below is an example of how to declare a constant in PostgreSQL called vSiteID .

This would declare a constant called vSiteID as an integer data type and assign an initial value of 50. Because this variable is declared using the CONSTANT keyword, you can not change its value after initializing the variable.

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PostgreSQL Tutorial: PL/pgSQL Variables

August 4, 2023

Summary : in this tutorial, you will learn various techniques to declare PL/pgSQL variables.

Table of Contents

Introduction to variables in PL/pgSQL

A variable is a meaningful name of a memory location. A variable holds a value that can be changed through the block . A variable is always associated with a particular data type .

Before using a variable, you must declare it in the declaration section of the PL/pgSQL block .

The following illustrates the syntax of declaring a variable.

In this syntax:

• First, specify the name of the variable. It is a good practice to assign a meaningful name to a variable. For example, instead of naming a variable i you should use index or counter .
• Second, associate a specific data type with the variable. The data type can be any valid data type such as integer , numeric , varchar , and char .
• Third, optionally assign a default value to a variable. If you don’t do so, the initial value of the variable is NULL .

Note that you can use either := or = assignment operator to initialize and assign a value to a variable.

The following example illustrates how to declare and initialize variables:

The counter variable is an integer that is initialized to 1

The first_name and last_name are varchar(50) and initialized to 'John' and 'Doe' string constants.

The type of payment is numeric and its value is initialized to 20.5

Variable initialization timing

PostgreSQL evaluates the default value of a variable and assigns it to the variable when the block is entered. For example:

Here is the output:

In this example:

• First, declare a variable whose default value is initialized to the current time.
• Second, print out the value of the variable and pass the execution in 10 seconds using the pg_sleep() function.
• Third, print out the value of the created_at variable again.

As shown clearly from the output, the value of the created_at is only initialized once when the block is entered.

Copying data types

The %type provides the data type of a table column or another variable. Typically, you use the %type to declare a variable that holds a value from the database or another variable.

The following illustrates how to declare a variable with the data type of a table column:

And the following shows how to declare a variable with the data type of another variable:

See the following film table from the sample database:

This example uses the type copying technique to declare variables that hold values which come from the film table:

This example declared two variables:

• The film_title variable has the same data type as the title column in the film table from the sample database .
• The featured_title has the same data type as the data type of the film_title variable.

By using type copying feature, you get the following advantages:

• First, you don’t need to know the type of the column or reference that you are referencing.
• Second, if the data type of the referenced column name (or variable) changes, you don’t need to change the definition of the function.

Variables in block and subblock

When you declare a variable in a subblock which hs the same name as another variable in the outer block, the variable in the outer block is hidden in the subblock.

In case you want to access a variable in the outer block, you use the block label to qualify its name as shown in the following example:

• First, declare a variable named counter in the outer_block .
• Next, declare a variable with the same name in the subblock.
• Then, before entering into the subblock, the value of the counter is one. In the subblock, we increase the value of the counter to ten and print it out. Notice that the change only affects the counter variable in the subblock.
• After that, reference the counter variable in the outer block using the block label to qualify its name outer_block.counter .
• Finally, print out the value of the counter variable in the outer block, its value remains intact.

In this tutorial, you have learned the various ways to declare PL/pgSQL variables.

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PostgreSQL – Variables

In PostgreSQL , a variable is a meaningful name for a memory location. A variable holds a value that can be changed through the block or function. A variable is always associated with a particular data type . Before using a variable, you must declare it in the declaration section of the PostgreSQL Block. The following illustrates the syntax of declaring a variable.

Let’s analyze the above syntax:

• First, specify the name of the variable. It is a good practice to assign a meaningful name to a variable. For example, instead of naming a variable “i “ one should use index or counter .
• Second, associate a specific data type with the variable. The data type can be any valid PostgreSQL data type such as INTEGER , NUMERIC , VARCHAR , and  CHAR .
• Third, optionally assign a default value to a variable. If you don’t, the initial value of the variable is initialized to NULL .

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Home » PostgreSQL PL/pgSQL » PL/pgSQL Variables

PL/pgSQL Variables

Summary : in this tutorial, you will learn about PL/pgSQL variables and various ways to declare them

Introduction to PL/pgSQL variables

In PL/pgSQL, variables are placeholders for storing data within a block . These variables can hold values of various types such as integers, booleans, text, and more.

Variables allow you to hold values for calculations, store query results, and so on.

Before using variables, you must declare them in the declaration section of a block.

Variables are scoped to the block in which they’re declared. It means that variables are accessible only within the block and any nested blocks.

The following illustrates the syntax of declaring a variable.

In this syntax:

• First, specify the name of the variable. It is a good practice to assign a meaningful name to a variable. For example, instead of naming a variable i you should use index or counter .
• Second, associate a specific data type with the variable. The data type can be any valid data type such as integer , numeric , varchar , and  char .
• Third, optionally assign a default value to the variable. If you don’t do so, the initial value of the variable is NULL .

Please note that you can use either := or = assignment operator to set an initial value for a variable.

To assign a value to a variable, you can use the assignment operator (=) as follows:

Alternatively, you can use the := assignment operator:

Basic PL/pgSQL variable example

1) declare variables.

The following example shows how to declare and initialize variables:

How it works.

First, declare four variables in the declaration part of the block:

• The counter variable is an integer with an initial value of 1.
• The first_name and last_name are varchar(50) with the initial values of 'John' and 'Doe' respectively.
• The payment variable has the numeric type with the initial value 20.5 .

Second, display the values of the variables using the raise notice statement.

2) Assign values to variables

The following example shows how to assign a value to a variable:

First, declare a variable in the declaration block:

Second, split a string literal into two parts using a space, return the first part, and assign it to the first_name variable:

Third, display the value of the first_name variable using the raise notice statement:

Variable initialization timing

PostgreSQL evaluates the initial value of a variable and assigns it when the block is entered. For example:

Here is the output:

In this example:

• First, declare a variable created_at and initialize its value to the current time.
• Second, display the variable.
• Third, pause the execution for 3 seconds using the pg_sleep() function.
• Finally, display the value of the created_at variable again.

The output indicates that the value of the created_at variable is only initialized once when the block is entered.

Copying data types

The %type provides the data type of a table column or another variable. Typically, you use the %type to declare a variable that holds a value from the database or another variable.

The following illustrates how to declare a variable with the data type of a table column:

The following shows how to declare a variable with the data type of another variable:

We’ll use the following film table from the sample database :

This example uses the type-copying technique to declare variables that hold values that come from the film table:

In this example, we declare two variables:

• The film_title variable has the same data type as the title column in the film table from the sample database .
• The featured_title has the same data type as the data type of the film_title variable.

We use the select into statement to retrieve from the film_title column of the film table and assign it to the film_title variable.

Using the type-copying feature offers the following advantages:

• First, you don’t need to know the type of column or reference being accessed.
• Second, if the data type of the referenced column name (or variable) changes, you don’t need to change the block.

Variables in blocks and subblocks

When you declare a variable in a subblock with the same name as another variable in the outer block, the variable in the outer block is hidden within the subblock.

To access a variable in the outer block, you use the block label to qualify its name, as shown in the following example:

• First, declare a variable named counter in the outer_block .
• Next, declare a variable with the same name in the subblock.
• Then, before entering into the subblock, the value of counter is one. Within the subblock, we increase the value of the counter variable to ten and print it out. Note that this change only affects the counter variable within the subblock.
• After that, reference the counter variable in the outer block using the block label outer_block.counter .
• Finally, display the value of the counter variable in the outer block, its value remains unchanged.
• A variable is a named storage location with a data type that can hold a value.
• PostgreSQL evaluates the default value of a variable and assigns it to the variable when it enters the block.
• Declare variables and optionally an initial value to it in the declaration section of the block.

• How to Use Variables in PostgreSQL
• PostgreSQL Howtos

Use DECLARE to Declare Variables in PostgreSQL

Use returning to assign value to variables in postgresql.

This article will demonstrate how we can declare and assign values to variables in PostgreSQL.

Usually, you’ll need variables in PL/SQL script. In the section called DECLARE , you need to tell the script what your variable is and what was its type.

In PL/SQL, there are two parts. One is the declaration, and another is the script part, where standard SQL is written. The format is like the following.

Now, we have a table of students and their tasks. Our job is to find a student that matches some condition and raise notice for the student.

The table Students is like the following:

Suppose you want to store the student name and task information, where id equals 3 . Now, here’s a thing to mention, we don’t know the data type of the id, name, and task.

If the type is a mismatch, then an error might occur. To resolve this, we need to use <column_name>%type .

If you’re running this sort of PL/SQL for the first time, RAISE will not work, meaning nothing will be shown after the execution of the SQL script. To enable this, you need to perform the following command in your psql shell.

After setting this, you can see the output like this (after executing the PL/SQL command):

Here’s another keyword, INTO . It places the data of your selected columns to the respective variables.

You’ve seen that the ID is the SERIAL type data from the above table. So, it will increase by one after every insertion.

But during the insertion, we never know which id is being assigned to the current row.

So, let’s say you want to see the ID after the insert command to the student table. The command will be as follows:

Also, you can use multiple queries inside the PL/SQL begin to part. Then, you can use the variable to check some conditions and do some CRUD operations.

More information is available here in the official documentation.

I'm Shihab Sikder, a professional Backend Developer with experience in problem-solving and content writing. Building secure, scalable, and reliable backend architecture is my motive. I'm working with two companies as a part-time backend engineer.

Related Article - PostgreSQL Variable

• How to Print Variable in PostgreSQL
• How to Declare a Variable in a PostgreSQL Query

How to declare variables in PL/pgSQL stored procedures

Rajkumar Raghuwanshi

SUMMARY: This article covers how stored procedures can make use of variables to be more functional and useful. After defining PL/pgSQL, stored procedures, and variables, it provides examples of how variables can be used.

The title of this post makes use of 3 terms: PL/pgSQL, stored procedure, and variable. Let’s start with a basic understanding of them.

PL/pgSQL : An abbreviation for Procedure Language/PostgreSQL. It is a procedural language that provides the ability to perform more complex operations and computations than SQL.

Stored Procedure: A block for SQL statements combined together under a name and saved in database which can be called on multiple times when needed.

Variable: A variable holds a value that can be changed through the block. It is always associated with a datatype. 

Now let’s try to understand these with examples.

Stored procedures include functions, procedures, triggers, and other objects that can be saved in databases. Below is a simple example for a stored procedure “Procedure”:

In this example, an SQL statement, which upon call prints “Procedure example1 called,” is saved under the name example1 and can be called multiple times as needed.

The example has a fixed message which it prints upon call. To make the function more dynamic and useful, we can use different types of variables and assign values to them at compile time as well at run time.

A variable must be declared in the declaration section of the PL/pgSQL block. Declaration syntax for a variable is: “ variable_name data_type [:=value/constant/expression]; ”

Variable_name: This can be any meaningful name or whatever the user wants.

Data_type: PostgreSQL supports data types like integer, numeric, varchar, and text, or it can be a %TYPE or %ROWTYPE. Here is a list of PostgreSQL supported data types: https://www.postgresql.org/docs/current/datatype.html .

Variable Assignment: Any value as accepted by data type, constant, or expression can be assigned to the variable. This part is optional. 

The user can print variable values by using RAISE NOTICE/EXCEPTION and “%” as a placeholder to be replaced by the variable value.

Let’s see an example for variable declaration and display:

The variable can also be of a column type or a row type of a table. These can be declared with data type as %TYPE and %ROWTYPE. Here is an example:

In this example the data type of the variable “eid_var” is declared by reference to the “eid” column’s data type in the “emp” table As output the user wants to return a complete row (all columns) of the “emp” table, so the variable “result” is declared as a reference to a whole row type of the “emp” table.

Another point to notice is that the “result” variable is assigned at runtime by using the result set of SELECT * INTO.

Another way to use %ROWTYPE in PostgreSQL variables is using RECORD as the data type of a variable. Below is the same example as above, but displaying “emp” table data using RECORD type.

In the same way, the user can use variables in other stored procedures like function and triggers.

Reference Links:

https://www.postgresql.org/docs/current/datatype.html

https://www.postgresql.org/docs/current/plpgsql-declarations.html

https://www.postgresql.org/docs/current/sql-createprocedure.html

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How To Declare A Variable In PostgreSQL

Faruk Erdem March 11, 2024 PostgreSQL

This PostgreSQL tutorial explains How To Declare A Variable In PostgreSQL with syntax and examples.

By declaring PostgreSQL Variables, sometimes we may need to use the values we receive from outside in operations such as insert, update and delete.

We can use variables when writing a Stored Procedure or Function.

First, let’s talk about the do method.

To declare a variable, we need to start with DO$$.

In the declare section or between the “begin end” blocks, we write the name and data type of our variable and define its value with “:=”.

The output of the variable can be printed on the screen by typing the variable declared with the ‘%’ sign after the RAISE NOTICE.

In RAISE NOTICE, after writing what you want to write before the variable inside the quotation marks, you need to write the % sign since we are using a single variable.

You can use it for multiple variables as follows.

Another different use is to declare session-based variables.

Example usage is as follows.

In the above example, it will bring the record in the veliler table according to the variable value entered.

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Declaring and Assigning Variables in PostgreSQL: A Troubleshooting Guide

Abstract: Having trouble declaring and assigning variables in PostgreSQL? Learn about common error messages and how to troubleshoot them in this guide.

Declaring and Assigning Variables in PostgreSQL: Troubleshooting Guide

In this article, we will explore how to declare and assign variables in PostgreSQL, as well as troubleshoot common issues that may arise. We will cover key concepts, applications, and the significance of declaring and assigning variables in PostgreSQL. This guide is aimed at those who have some experience with PostgreSQL and are looking to deepen their understanding of this important feature.

Key Concepts

In PostgreSQL, variables are used to store values that can be referenced and used in SQL statements. There are two types of variables in PostgreSQL: plpgsql variables and sql variables. plpgsql variables are used in PL/pgSQL functions and procedures, while sql variables are used in SQL statements.

To declare a variable in PostgreSQL, you can use the DECLARE statement followed by the variable name and data type. For example:

To assign a value to a variable, you can use the := operator. For example:

Troubleshooting Common Issues

One common issue that may arise when trying to declare and assign a variable in PostgreSQL is the following error message:

This error occurs because the := operator is not supported in sql variables. Instead, you should use the = operator. For example:

Applications and Significance

Declaring and assigning variables in PostgreSQL is an important feature that has many applications. For example, you can use variables to store intermediate results in complex queries, or to pass values between different parts of a PL/pgSQL function or procedure. By understanding how to declare and assign variables in PostgreSQL, you will be able to write more efficient and effective SQL statements.

• Variables in PostgreSQL are used to store values that can be referenced and used in SQL statements.
• There are two types of variables in PostgreSQL: plpgsql variables and sql variables.
• To declare a variable in PostgreSQL, use the DECLARE statement followed by the variable name and data type.
• To assign a value to a variable, use the = operator for sql variables and the := operator for plpgsql variables.
• Understanding how to declare and assign variables in PostgreSQL is important for writing efficient and effective SQL statements.
• PostgreSQL PL/pgSQL Declarations
• PostgreSQL PL/pgSQL Variables
• PostgreSQL PL/pgSQL SQL Statements

Tags: :  PostgreSQL variables SQL database development

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PostgreSQL SELECT INTO Variable: A Guide for Beginners

Psql Select Into Variable: A Powerful Tool for Data Manipulation

The `psql select into variable` command is a powerful tool for data manipulation in PostgreSQL. It allows you to select data from a table or view and store it in a variable, which can then be used in other queries or commands. This can be a great way to save time and effort, especially when you need to perform the same operation on multiple rows of data.

In this article, we will take a closer look at the `psql select into variable` command. We will discuss the syntax of the command, and we will show you how to use it to perform a variety of data manipulation tasks. We will also provide some tips and tricks to help you get the most out of this powerful tool.

So if you’re looking for a way to save time and effort on your data manipulation tasks, then be sure to read on!

In this tutorial, you will learn how to use the `psql select into variable` statement to assign the results of a SELECT query to a variable in the PostgreSQL command line interface (CLI). This can be useful for storing the results of a query in a variable for later use, or for passing the results of a query to another command.

What is psql select into variable?

The `psql select into variable` statement is used to assign the results of a SELECT query to a variable in the PostgreSQL CLI. The syntax for a psql select into variable statement is as follows:

SELECT * INTO my_variable FROM my_table;

In this example, the `*` wildcard is used to select all columns from the `my_table` table. The results of the SELECT query are then assigned to the variable `my_variable`.

How to use psql select into variable?

To use psql select into variable, first open a psql session and connect to a database. Then, type the following command to create a variable called `my_variable`:

CREATE VARIABLE my_variable TEXT;

This command creates a variable called `my_variable` that can store a string value.

Next, type the following command to assign the results of a SELECT query to the variable `my_variable`:

This command will select all columns from the `my_table` table and assign the results to the variable `my_variable`.

Now, you can use the variable `my_variable` in any subsequent commands. For example, you could type the following command to print the contents of the variable `my_variable`:

\echo $my_variable

This command will print the following output:

| column1 | column2 | |———|———| | value1 | value2 |

As you can see, the `psql select into variable` statement is a powerful tool that can be used to store the results of a SELECT query in a variable for later use.

Here are some additional examples of how to use the `psql select into variable` statement:

• To select all rows from the `my_table` table and assign the results to the variable `my_variable`, you could use the following command:
• To select only the `column1` and `column2` columns from the `my_table` table and assign the results to the variable `my_variable`, you could use the following command:

SELECT column1, column2 INTO my_variable FROM my_table;

• To select all rows from the `my_table` table where the `column1` column is equal to `value1` and assign the results to the variable `my_variable`, you could use the following command:

SELECT * INTO my_variable FROM my_table WHERE column1 = ‘value1’;

In this tutorial, you learned how to use the `psql select into variable` statement to assign the results of a SELECT query to a variable in the PostgreSQL CLI. This can be useful for storing the results of a query in a variable for later use, or for passing the results of a query to another command.

3. Examples of psql select into variable

The psql select into variable statement can be used to assign the results of a SELECT query to a variable. This can be useful for storing the results of a query for later use, or for passing the results of a query to another query.

The following are some examples of psql select into variable statements:

• To select all the rows from the `users` table and assign them to the variable `my_users`:

SELECT * INTO my_users FROM users;

• To select the `first_name` and `last_name` columns from the `users` table and assign them to the variable `my_name`:

SELECT first_name, last_name INTO my_name FROM users;

• To select the `email` column from the `users` table and assign it to the variable `my_email`:

SELECT email INTO my_email FROM users;

4. Limitations of psql select into variable**

The psql select into variable statement has a few limitations, including:

• The variable name must be a valid PostgreSQL identifier.
• The variable type must be compatible with the data types of the columns in the SELECT query.
• The variable cannot be used in a subquery.

For more information on the limitations of psql select into variable, please refer to the PostgreSQL documentation.

5. Tips for using psql select into variable

The following are some tips for using psql select into variable:

• Use the `AS` keyword to alias the columns in the SELECT query. This can make it easier to use the variable in subsequent queries.
• Use the `WITH` clause to create a temporary table from the results of the SELECT query. This can be useful if you need to use the results of the query multiple times.
• Use the `ORDER BY` clause to sort the results of the query. This can be useful if you need to process the results in a specific order.
• Use the `LIMIT` and `OFFSET` clauses to limit the number of rows that are returned by the query. This can be useful if you only need to process a subset of the results.

The psql select into variable statement is a powerful tool that can be used to store the results of a SELECT query in a variable. This can be useful for storing the results of a query for later use, or for passing the results of a query to another query. However, there are some limitations to the psql select into variable statement, so it is important to be aware of these before using it.

Q: What is the psql select into variable command?

A: The psql select into variable command allows you to store the results of a SELECT statement into a variable. This can be useful for saving the results of a query for later use, or for passing the results to another command.

Q: How do I use the psql select into variable command?

A: The syntax for the psql select into variable command is as follows:

SELECT * INTO VARIABLE FROM ;

For example, the following command would store the results of a SELECT statement into a variable called `results`:

SELECT * INTO VARIABLE results FROM my_table;

Q: What types of data can I store in a psql variable?

A: You can store any type of data in a psql variable, including strings, numbers, and dates.

Q: Can I use the psql select into variable command with multiple tables?

A: Yes, you can use the psql select into variable command with multiple tables. To do this, simply specify the tables in the FROM clause, separated by commas.

Q: What are some of the advantages of using the psql select into variable command?

There are a number of advantages to using the psql select into variable command. These include:

• Simplicity: The psql select into variable command is very simple to use.
• Flexibility: The psql select into variable command can be used with any type of data.
• Reusability: The results of a psql select into variable command can be reused in other queries or commands.

Q: What are some of the disadvantages of using the psql select into variable command?

There are a few disadvantages to using the psql select into variable command. These include:

• Performance: The psql select into variable command can be slower than other methods of storing data.
• Security: The psql select into variable command can be used to store sensitive data, which could pose a security risk.

Q: When should I use the psql select into variable command?

You should use the psql select into variable command when you need to store the results of a SELECT statement for later use. This can be useful for saving the results of a query for later analysis, or for passing the results to another command.

Q: What are some other ways to store the results of a SELECT statement?

There are a number of other ways to store the results of a SELECT statement. These include:

• Using a temporary table: You can create a temporary table to store the results of a SELECT statement. This is a good option if you need to store the results of a query for a long period of time.
• Using a file: You can export the results of a SELECT statement to a file. This is a good option if you need to store the results of a query in a format that can be easily read by other programs.

We hope that this blog post has been helpful. If you have any questions or feedback, please feel free to reach out to us.

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Use variable as column name

I'm trying to create trigger in PostgreSQL 14:

Can I make a column name from the variable equipment_stat , or is that a bad idea?

update Here's how I did it

• dynamic-sql

• 2 Please provide a complete function definition, not just the rump that is invalid without the header. And always your version of Postgres. Also show the trigger definition. And clarify your question, please. "Can I make a column name from the 'equipment_stat' variable" ... do you want to use the value of equipment_stat as column name in the UPDATE command? There may be a simple pure SQL solution for this. Better yet, you should probably work with a normalized table design. –  Erwin Brandstetter Commented May 7, 2022 at 16:06
• @ErwinBrandstetter,Yes I want to use the value of the equipment_stat variable, and I couldn't find a way to do that. If you can do it I would be very grateful. –  Sevas Commented May 7, 2022 at 19:35
• 1 You would need dynamic SQL with EXECUTE . But I am hesitant to even show a solution because your approach is backwards in multiple ways. You shouldn't UPDATE the same row repeatedly. Much less the triggering row itself. And it makes no sense to RETURN NEW; in an AFTER trigger. You probably should use a BEFORE trigger and just assign new values to each NEW.column . Your IF condition also looks suspicious. Guess that's there to shoe in both INSERT and UPDATE case into the same trigger. Start by splitting both cases to separate triggers ... –  Erwin Brandstetter Commented May 7, 2022 at 20:58
• Related: dba.stackexchange.com/a/144395/3684 or dba.stackexchange.com/a/105928/3684 –  Erwin Brandstetter Commented May 7, 2022 at 21:11
• @ErwinBrandstetter, Thanks for the explanation and guidance. –  Sevas Commented May 8, 2022 at 10:03

I can't let you do this. :)

Don't repeatedly UPDATE the triggering row. That's hugely inefficient and error-prone.

Use a BEFORE trigger instead, where you can simply assign new values to columns of the triggering row before writing it to the table.

Only covering the INSERT case. Extend to UPDATE accordingly.

Simplistic function with loop

Much better than expensive multiple UPDATE s. But still inefficient. You don't need the loop with multiple assignment at all.

Much smarter jsonb_populate_record()

At best, one straight invocation of jsonb_populate_record() is all you need:

• Use trigger to synchronize columns with fields in json column on insert or update

Additional keys in player_equipment_armor['stats'] that have no matching field in NEW are discarded automatically. And additional fields in NEW that have no mo match in player_equipment_armor['stats'] are kept as is.

If armor_stats['stats'] needs to be applied to remove keys, you can do that, too:

db<>fiddle here

This removes all keys that are not present armor_stats['stats'] before calling jsonb_populate_record() . See:

• Select rows which are not present in other table

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43.11.  PL/pgSQL under the Hood #

This section discusses some implementation details that are frequently important for PL/pgSQL users to know.

43.11.1. Variable Substitution #

SQL statements and expressions within a PL/pgSQL function can refer to variables and parameters of the function. Behind the scenes, PL/pgSQL substitutes query parameters for such references. Query parameters will only be substituted in places where they are syntactically permissible. As an extreme case, consider this example of poor programming style:

The first occurrence of foo must syntactically be a table name, so it will not be substituted, even if the function has a variable named foo . The second occurrence must be the name of a column of that table, so it will not be substituted either. Likewise the third occurrence must be a function name, so it also will not be substituted for. Only the last occurrence is a candidate to be a reference to a variable of the PL/pgSQL function.

Another way to understand this is that variable substitution can only insert data values into an SQL command; it cannot dynamically change which database objects are referenced by the command. (If you want to do that, you must build a command string dynamically, as explained in Section 43.5.4 .)

Since the names of variables are syntactically no different from the names of table columns, there can be ambiguity in statements that also refer to tables: is a given name meant to refer to a table column, or a variable? Let's change the previous example to

Here, dest and src must be table names, and col must be a column of dest , but foo and bar might reasonably be either variables of the function or columns of src .

By default, PL/pgSQL will report an error if a name in an SQL statement could refer to either a variable or a table column. You can fix such a problem by renaming the variable or column, or by qualifying the ambiguous reference, or by telling PL/pgSQL which interpretation to prefer.

The simplest solution is to rename the variable or column. A common coding rule is to use a different naming convention for PL/pgSQL variables than you use for column names. For example, if you consistently name function variables v_ something while none of your column names start with v_ , no conflicts will occur.

Alternatively you can qualify ambiguous references to make them clear. In the above example, src.foo would be an unambiguous reference to the table column. To create an unambiguous reference to a variable, declare it in a labeled block and use the block's label (see Section 43.2 ). For example,

Here block.foo means the variable even if there is a column foo in src . Function parameters, as well as special variables such as FOUND , can be qualified by the function's name, because they are implicitly declared in an outer block labeled with the function's name.

Sometimes it is impractical to fix all the ambiguous references in a large body of PL/pgSQL code. In such cases you can specify that PL/pgSQL should resolve ambiguous references as the variable (which is compatible with PL/pgSQL 's behavior before PostgreSQL 9.0), or as the table column (which is compatible with some other systems such as Oracle ).

To change this behavior on a system-wide basis, set the configuration parameter plpgsql.variable_conflict to one of error , use_variable , or use_column (where error is the factory default). This parameter affects subsequent compilations of statements in PL/pgSQL functions, but not statements already compiled in the current session. Because changing this setting can cause unexpected changes in the behavior of PL/pgSQL functions, it can only be changed by a superuser.

You can also set the behavior on a function-by-function basis, by inserting one of these special commands at the start of the function text:

These commands affect only the function they are written in, and override the setting of plpgsql.variable_conflict . An example is

In the UPDATE command, curtime , comment , and id will refer to the function's variable and parameters whether or not users has columns of those names. Notice that we had to qualify the reference to users.id in the WHERE clause to make it refer to the table column. But we did not have to qualify the reference to comment as a target in the UPDATE list, because syntactically that must be a column of users . We could write the same function without depending on the variable_conflict setting in this way:

Variable substitution does not happen in a command string given to EXECUTE or one of its variants. If you need to insert a varying value into such a command, do so as part of constructing the string value, or use USING , as illustrated in Section 43.5.4 .

Variable substitution currently works only in SELECT , INSERT , UPDATE , DELETE , and commands containing one of these (such as EXPLAIN and CREATE TABLE ... AS SELECT ), because the main SQL engine allows query parameters only in these commands. To use a non-constant name or value in other statement types (generically called utility statements), you must construct the utility statement as a string and EXECUTE it.

43.11.2. Plan Caching #

The PL/pgSQL interpreter parses the function's source text and produces an internal binary instruction tree the first time the function is called (within each session). The instruction tree fully translates the PL/pgSQL statement structure, but individual SQL expressions and SQL commands used in the function are not translated immediately.

As each expression and SQL command is first executed in the function, the PL/pgSQL interpreter parses and analyzes the command to create a prepared statement, using the SPI manager's SPI_prepare function. Subsequent visits to that expression or command reuse the prepared statement. Thus, a function with conditional code paths that are seldom visited will never incur the overhead of analyzing those commands that are never executed within the current session. A disadvantage is that errors in a specific expression or command cannot be detected until that part of the function is reached in execution. (Trivial syntax errors will be detected during the initial parsing pass, but anything deeper will not be detected until execution.)

PL/pgSQL (or more precisely, the SPI manager) can furthermore attempt to cache the execution plan associated with any particular prepared statement. If a cached plan is not used, then a fresh execution plan is generated on each visit to the statement, and the current parameter values (that is, PL/pgSQL variable values) can be used to optimize the selected plan. If the statement has no parameters, or is executed many times, the SPI manager will consider creating a generic plan that is not dependent on specific parameter values, and caching that for re-use. Typically this will happen only if the execution plan is not very sensitive to the values of the PL/pgSQL variables referenced in it. If it is, generating a plan each time is a net win. See PREPARE for more information about the behavior of prepared statements.

Because PL/pgSQL saves prepared statements and sometimes execution plans in this way, SQL commands that appear directly in a PL/pgSQL function must refer to the same tables and columns on every execution; that is, you cannot use a parameter as the name of a table or column in an SQL command. To get around this restriction, you can construct dynamic commands using the PL/pgSQL EXECUTE statement — at the price of performing new parse analysis and constructing a new execution plan on every execution.

The mutable nature of record variables presents another problem in this connection. When fields of a record variable are used in expressions or statements, the data types of the fields must not change from one call of the function to the next, since each expression will be analyzed using the data type that is present when the expression is first reached. EXECUTE can be used to get around this problem when necessary.

If the same function is used as a trigger for more than one table, PL/pgSQL prepares and caches statements independently for each such table — that is, there is a cache for each trigger function and table combination, not just for each function. This alleviates some of the problems with varying data types; for instance, a trigger function will be able to work successfully with a column named key even if it happens to have different types in different tables.

Likewise, functions having polymorphic argument types have a separate statement cache for each combination of actual argument types they have been invoked for, so that data type differences do not cause unexpected failures.

Statement caching can sometimes have surprising effects on the interpretation of time-sensitive values. For example there is a difference between what these two functions do:

In the case of logfunc1 , the PostgreSQL main parser knows when analyzing the INSERT that the string 'now' should be interpreted as timestamp , because the target column of logtable is of that type. Thus, 'now' will be converted to a timestamp constant when the INSERT is analyzed, and then used in all invocations of logfunc1 during the lifetime of the session. Needless to say, this isn't what the programmer wanted. A better idea is to use the now() or current_timestamp function.

In the case of logfunc2 , the PostgreSQL main parser does not know what type 'now' should become and therefore it returns a data value of type text containing the string now . During the ensuing assignment to the local variable curtime , the PL/pgSQL interpreter casts this string to the timestamp type by calling the textout and timestamp_in functions for the conversion. So, the computed time stamp is updated on each execution as the programmer expects. Even though this happens to work as expected, it's not terribly efficient, so use of the now() function would still be a better idea.

Submit correction

If you see anything in the documentation that is not correct, does not match your experience with the particular feature or requires further clarification, please use this form to report a documentation issue.

which symbol is used for variable assignment in postgresql

16. Here's an example of using a variable in plpgsql: create table test (id int); insert into test values (1); insert into test values (2); insert into test values (3); create function test_fn() returns int as $$. declare val int := 2; begin.

43.5.1. Assignment #. An assignment of a value to a PL/pgSQL variable is written as: variable { := | = } expression ; As explained previously, the expression in such a statement is evaluated by means of an SQL SELECT command sent to the main database engine. The expression must yield a single value (possibly a row value, if the variable is a ...

variable_name data_type [= expression]; Code language: PostgreSQL SQL dialect and PL/pgSQL (pgsql) In this syntax: First, specify the name of the variable. It is a good practice to assign a meaningful name to a variable. For example, instead of naming a variable i you should use index or counter. Second, associate a specific data type with the ...

In PostgreSQL, a variable is a meaningful name for a memory location. A variable holds a value that can be changed through the block or function. A variable is always associated with a particular data type. Before using a variable, you must declare it in the declaration section of the PostgreSQL Block. The following illustrates the syntax of ...

PostgreSQL operators are symbols or keywords that represent specific operations that can be performed on database tables and data. These operators can be used in SQL queries to perform various tasks such as comparison, arithmetic, logical, and string operations. ... we have explored the different types of operators available in PostgreSQL and ...

In the section called DECLARE, you need to tell the script what your variable is and what was its type. In PL/SQL, there are two parts. One is the declaration, and another is the script part, where standard SQL is written. The format is like the following. DO $$. DECLARE variable_name <TYPE>.

Variable assignment is done with PL/pgSQL's assignment operator ( := ), in the form of left_variable := right_variable , in which the value of the right variable is assigned to the left variable. Also valid is left_variable := expression , which assigns the left-hand variable the value of the expression on the right side of the assignment operator.

The main practical use for this is to assign a different name for variables with predetermined names, such as NEW or OLD within a trigger function. Examples: DECLARE prior ALIAS FOR old; updated ALIAS FOR new; Since ALIAS creates two different ways to name the same object, unrestricted use can be confusing. It's best to use it only for the ...

SQL has no support for variables, this is only possible in procedural languages (in Postgres that would e.g. be PL/pgSQL). The way to to this in plain SQL is to use a CTE (which is also a cross platform solution and not tied to any SQL dialect): with vars (foo) as ( values ('bar') ) select foo from vars;

Using the SET Command. The SET command allows you to assign values to variables in PostgreSQL. This method is straightforward and easy to use. Here's an example: SET my_variable = 'Hello, World!'; In this example, we have set the value of the my_variable to 'Hello, World!'.

The title of this post makes use of 3 terms: PL/pgSQL, stored procedure, and variable. Let's start with a basic understanding of them. PL/pgSQL: An abbreviation for Procedure Language/PostgreSQL. It is a procedural language that provides the ability to perform more complex operations and computations than SQL.

The precise syntax rules for each command are described in the PostgreSQL 7.3.21 Reference Manual. 1.1.1. Identifiers and Key Words. Tokens such as SELECT, UPDATE, or VALUES in the example above are examples of key words, that is, words that have a fixed meaning in the SQL language.

An assignment of a value to a PL/pgSQL variable is written as: variable { := | = } expression; . As explained previously, the expression in such a statement is evaluated by means of an SQL SELECT command sent to the main database engine. The expression must yield a single value (possibly a row value, if the variable is a row or record variable).

Here's how you can declare and use variables in PL/pgSQL: Declaration: You can declare a variable using the DECLARE statement within the body of your PL/pgSQL code block. You should specify the variable name, data type, and optionally an initial value. Initialization: You can initialize a variable when you declare it, or you can set its value ...

Variables in PostgreSQL are used to store values that can be referenced and used in SQL statements. There are two types of variables in PostgreSQL: plpgsql variables and sql variables. To declare a variable in PostgreSQL, use the DECLARE statement followed by the variable name and data type. To assign a value to a variable, use the = operator ...

Very hard to debug if you're unaware of the distinction between = and :=. Always use the the correct operator. 1 When using named notation in function calls, only := is the correct assignment operator. This applies to functions of all languages, not just PL/pgSQL, up to and including pg 9.4. See below.

43.11.2. Plan Caching #. The PL/pgSQL interpreter parses the function's source text and produces an internal binary instruction tree the first time the function is called (within each session). The instruction tree fully translates the PL/pgSQL statement structure, but individual SQL expressions and SQL commands used in the function are not ...

In PostgreSQL, variables are declared using the DECLARE statement. This statement allows you to define the name, data type, and initial value of a variable. Once declared, you can assign values to the variable using the := operator. For example, you can declare a variable called "count" of type integer and assign it a value of 0: DECLARE count ...

I did that, and it returned a value of null. But when I run the command: show log_destination alone, I can see some value being returned. Why is that the case?

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How to declare variable and assign values in Postgres

I have tried to declare a variable and assign value to it. But I am always getting error message with error code: SQL state: 42601

Example of a simple SQL statement written within PostgreSQL is as per below:

DECLARE dest_var TEXT;

dest_var = show log_destination;

Can anyone suggest on ways to overcome this problem?

Tried to google, search for tutorials on declaring variables in postgres

• 2 This has to happen inside a function or procedure. For plpgsql this is Function structure with more details here Declarations . –  Adrian Klaver Commented Jan 4 at 5:18
• Thanks for highlighting that @adrianKlaver. Now I am getting an error within the function that says: ERROR: column "show" does not exist LINE 1: dest_var := show log_destination. How can I solve this any idea? –  Abrar Commented Jan 4 at 6:34
• Put your content between quotes ': dest_var := 'show log_destination'; –  Frank Heikens Commented Jan 4 at 6:47
• I did that, and it returned a value of null. But when I run the command: show log_destination alone, I can see some value being returned. Why is that the case? Could it be because of the command being in quotations? –  Abrar Commented Jan 4 at 7:06
• 1 You can also select current_setting('log_destination') into dest_var; . Demo here . –  Zegarek Commented Jan 4 at 12:02

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• A puzzle from YOU to ME ;)
• Short story about soldiers who are fighting against an enemy which turns out to be themselves
• Is it problematic to define the line integral in terms of infinitesimals
• What was the submarine in the film "Ice Station Zebra"?
• What is a curate in English scone culture?
• proper way to write C code that injects message into /var/log/messages