调用时存储过程错误

Question

When I call my procedure, it return an error:

1064 - 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 'NULL' at line 1

How to fix it, do I have an error in my procedure code?

Here is my stored procedure :

DELIMITER $$
DROP PROCEDURE IF EXISTS `gamedb`.`ALIAS#SEARCH`$$
CREATE DEFINER=`root`@`localhost` PROCEDURE `ALIAS#SEARCH`(
  in section_id varchar(255),
  in category_id varchar(255),
  in content_id varchar(255)
)

BEGIN
declare q varchar(4000);
set @q = 'SELECT * FROM tbl_alias WHERE ALIAS_ACTIVE_STATUS=1';

IF section_id IS NOT NULL THEN
  set @q = concat(q,' AND ALIAS_SECTION_ID = ',section_id);
END IF;

IF category_id IS NOT NULL THEN
  set @q = concat(q,' AND ALIAS_CATEGORY_ID = ',category_id);
END IF;

IF content_id IS NOT NULL THEN
  set @q = concat(q,' AND ALIAS_CONTENT_ID = ',content_id);
END IF;

set @q= concat(q,' ORDER BY ALIAS_ID DESC');
prepare stmt from @q;

EXECUTE stmt;
DEALLOCATE PREPARE stmt;
END$$
DELIMITER ;

Answer 1

There several problems

1. Since you can PREPARE only from user variable, you don't need a local variable q

2. You're missing @ for @q variable when using CONCAT()

    set @q = concat(q,' AND ALIAS_SECTION_ID = ',section_id); ^ 

3. Since your IN parameters defined as VARCHAR you better quote their values when you build the query

That being said your SP might look like this

DELIMITER $$
CREATE PROCEDURE `ALIAS#SEARCH`(
  in section_id varchar(255),
  in category_id varchar(255),
  in content_id varchar(255)
)

BEGIN
  SET @q = 'SELECT * FROM tbl_alias WHERE ALIAS_ACTIVE_STATUS = 1';

  IF section_id IS NOT NULL THEN
    SET @q = CONCAT(@q, ' AND ALIAS_SECTION_ID = ''', section_id, '''');
  END IF;

  IF category_id IS NOT NULL THEN
    SET @q = CONCAT(@q, ' AND ALIAS_CATEGORY_ID = ''', category_id, '''');
  END IF;

  IF content_id IS NOT NULL THEN
    SET @q = CONCAT(@q, ' AND ALIAS_CONTENT_ID = ''', content_id, '''');
  END IF;

  SET @q = CONCAT(@q, ' ORDER BY ALIAS_ID DESC');

  PREPARE stmt FROM @q;
  EXECUTE stmt;
  DEALLOCATE PREPARE stmt;
END$$
DELIMITER ;