SET

The SET statement assigns a value to a variable for the current session. Variables set this way live for the life of the connection and are visible to SHOW VARIABLES.

Basic Syntax

SET @variable_name = value;
SET @@system_variable = value;

Variable Kinds

Prefix	Kind	Who may set it
`@name`	User variable — yours to define, carries no meaning to the engine	Anyone
`@@name`	System variable — changes engine behaviour	Depends on the variable

A bare name with no prefix is treated as a system variable, and setting one you are not permitted to change is refused:

User does not have permission to set variable `sql_select_limit`

Examples

Set a User Variable

SET @cutoff = '2026-01-01';

SELECT * FROM orders WHERE created_at >= @cutoff;

Set a System Variable

SET @@sql_select_limit = 1000;

Notes

Variables are per-session. A new connection starts from the engine defaults, and nothing set this way persists beyond the session.
Use SHOW VARIABLES to list the variables visible to the session, along with each one's value, type, owner (INTERNAL or USER) and visibility.
Some system variables are restricted to platform administrators; setting one you do not hold permission for is refused rather than quietly ignored.