SET ? DECLARE

http://dev.mysql.com/doc/refman/5.7/en/declare-local-variable.html

http://dev.mysql.com/doc/refman/5.7/en/set-variable.html

SET Syntax for Variable Assignment

Local Variable DECLARE Syntax

DECLARE var_name [, var_name] ... type [DEFAULT value]
This statement declares local variables within stored programs.

SET variable_assignment [, variable_assignment] ...

variable_assignment:
      user_var_name = expr
    | param_name = expr
    | local_var_name = expr
    | [GLOBAL | SESSION]
        system_var_name = expr
    | [@@global. | @@session. | @@]
        system_var_name = expr

SET syntax for variable assignment enables you to assign values to different types of variables that affect the operation of the server or clients:

• System variables. See Section 6.1.5, “Server System Variables”. System variables also can be set at server startup, as described in Section 6.1.6, “Using System Variables”. (To display system variable names and values, use the SHOW VARIABLES statement; see Section 14.7.5.39, “SHOW VARIABLES Syntax”.)

• User-defined variables. See Section 10.4, “User-Defined Variables”.

• Stored procedure and function parameters, and stored program local variables. See Section 14.6.4, “Variables in Stored Programs”.