What does := mean in sql

In SQL, the ":=" assignment operator is used to store the result of an expression in a specified variable. It immediately assigns the value of the expression on the right side of the equal sign to the variable on the left side of the equal sign. Additionally, := is available in any SQL statement (such as a stored procedure) and is an alias for the SET statement, but it cannot assign a value to a column or table.

The := operator in SQL

The := assignment operator in SQL is used in variables Store the value. The assignment operator stores the result of the expression on the right side of the equal sign in the variable specified on the left side of the equal sign.

Usage

:= The basic form of the syntax is:

<code>变量 := 表达式</code>

where:

• The variable is a storage expression the result variable.
• An expression is an SQL statement that produces a value to be stored.

Example

The following query creates a variable named total_sales, which stores the sales table The sum of all sales:

DECLARE total_sales INT;
SET total_sales := (SELECT SUM(sale_amount) FROM sales);

Features

• := is an immediate assignment operator, which means that the value of the variable is immediately when the assignment statement is executed Change.
• You can use := in any SQL statement, including stored procedures, functions, and triggers.
• := is an alias for the SET statement and can be used for assignment.

Notes

• Variables must be declared before use.
• The expression must produce a value compatible with the variable data type.
• := cannot be used to assign values ​​to columns or tables.

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