MySQL Select into variable

问题

I want to further use in the procedure the values I get from a select into execution but can't figure out how to do it.

As a test I wrote the following but cannot use the v_1, v_2 or v_3 variables for further logic as they don't take the values 1,2 & 3 as i expected...

DROP PROCEDURE IF EXISTS MPT_testing; DELIMITER //  CREATE PROCEDURE MPT_testing() READS SQL DATA BEGIN

  DECLARE v_1 INT;   DECLARE v_2 INT;   DECLARE v_3 INT;
     SET @sql=CONCAT('SELECT 1,2 into v_1, v_2');   PREPARE s1 FROM @sql;   EXECUTE s1;   DEALLOCATE PREPARE s1;

  SET v_3 = v_1 + v_2;

  SELECT v_3;

END //

DELIMITER ;

Can somebody help here please?

thanks, Leo

回答1:

Try changing 'SELECT 1,2 into v_1, v_2' to

'SELECT @v_1:=1, @v_2:=2'

or at least make sure you use @ whenever referencing your vars. see this thread for more info: SELECT INTO Variable in MySQL DECLARE causes syntax error?

回答2:

If you do not need the dynamic SQL inside your procedure, you can simpler syntax:

DECLARE v_1 INT;   DECLARE v_2 INT;   DECLARE v_3 INT;

SELECT 1,2 into v_1, v_2;
SET v_3 = v_1 + v_2;
SELECT v_3;

Using normal variables declared inside stored procedure are safer than the user-defined variables (@-variables) as a call to another stored procedure may change your user-defined variable value.

回答3:

You need to modify little code to work properly see my modification

DECLARE v_1 INT;
DECLARE v_2 INT;
DECLARE v_3 INT;

SET @sql=CONCAT('SELECT 1,2 into @v1, @v2');
PREPARE s1 FROM @sql;
EXECUTE s1;

SELECT @v1, @v2 INTO v_1, v_2;
SET v_3 = v_1 + v_2;
SELECT v_3;

DEALLOCATE PREPARE s1;

来源：https://stackoverflow.com/questions/13351479/mysql-select-into-variable