SET var_name = expr [, var_name = expr] ...
SET statement in stored programs is an extended version of the general
SET statement. Referenced variables may be ones declared inside a stored program, global system variables, or user-defined variables.
SET statement in stored programs is implemented as part of the
pre-existing SET syntax. This allows an extended syntax of
b=y, ... where different variable types (locally declared variables,
global and session server variables, user-defined variables) can be
mixed. This also allows combinations of local variables and some
options that make sense only for system variables; in that case, the
options are recognized but ignored.
When setting several variables using the columns returned by a query,
SELECT INTO should be preferred.
To set many variables to the same value, the
LAST_VALUE( ) function can be used.
Below is an example of how a user-defined variable may be set:
SET @x = 1;