MySQL PREPARE statement in stored procedures

Question

I have this sql file:

USE mydb;

DROP PROCEDURE IF EXISTS execSql;
DELIMITER //
CREATE PROCEDURE execSql (
                     IN sqlq VARCHAR(5000)
                      ) COMMENT 'Executes the statement'
BEGIN
  PREPARE stmt FROM sqlq;
  EXECUTE stmt;
  DEALLOCATE PREPARE stmt;
END //
DELIMITER ;          

When I try to run it with

# cat file.sql | mysql -p

I get

ERROR 1064 (42000) at line 6: You have an error in your SQL syntax; check the manual
that corresponds to your MySQL server version for the right syntax to use near 'sqlq;
  EXECUTE stmt;
  DEALLOCATE PREPARE stmt;
  END' at line 5

What am I doing wrong?

Answer 1

you can only prepare and execute sql that's a string literal or a user variable that contains the text of the statement. try

USE mydb;

DROP PROCEDURE IF EXISTS execSql;
DELIMITER //
CREATE PROCEDURE execSql (
                 IN sqlq VARCHAR(5000)
                  ) COMMENT 'Executes the statement'
BEGIN
  SET @sqlv=sqlq;
  PREPARE stmt FROM @sqlv;
  EXECUTE stmt;
  DEALLOCATE PREPARE stmt;
END //
DELIMITER ;      

Answer 2

You can use Concatenate, PREPARE and EXECUTE statements as bellow..

CREATE DEFINER=`products`@`localhost` PROCEDURE `generateMeritList`(
   IN `mastercategory_id` INT(11), 
   IN `masterschools_id` INT(11)
 )
 NO SQL
 begin

  declare total int default 0;
  declare conditions varchar(255) default ''; 
  declare finalQuery varchar(60000) default '';

if mastercategory_id > 0 THEN
    SET conditions =  CONCAT(' and app.masterschools_id = ', mastercategory_id);
end if;

SET @finalQuery = CONCAT(
 "SELECT * FROM applications app INNER JOIN masterschools school ON school.id = app.masterschools_id
WHERE 
 (app.status = 'active'", conditions, " LIMIT ",total); 

 PREPARE stmt FROM @finalQuery;
 EXECUTE stmt;
 DEALLOCATE PREPARE stmt;

end