如何在MySQL存储过程中使用准备好的语句？

我正在使用mysql，我需要以某种方式在以后的查询中使用由prepared语句返回的curid列。我使用准备好的语句，因为如我所读，这是将变量传递给LIMIT子句的唯一方法。我在这里有此存储过程：

DROP PROCEDURE IF EXISTS fixbalance;
CREATE PROCEDURE fixbalance (userid INT)
  BEGIN
  DECLARE i INT DEFAULT 0;
  DECLARE balance INT DEFAULT 0;
  DECLARE idcnt INT;

  SET idcnt = (SELECT COALESCE(COUNT(id), 0) 
               FROM coupon_operations 
               WHERE user_id = userid);
  IF idcnt <> 0 THEN
    WHILE i <= idcnt DO
      BEGIN
        SET @iter = i;
        SET @user_id = userid; 
        SET @sql = CONCAT('SELECT id AS curid 
                           FROM coupon_operations 
                           WHERE user_id = ? 
                           ORDER BY id ASC 
                           LIMIT ?, 1');
        PREPARE stmt FROM @sql;
        EXECUTE stmt USING @user_id, @iter;
        DEALLOCATE PREPARE stmt;
        SET balance = balance + (SELECT points 
                                 FROM coupon_operations 
                                 WHERE user_id = @user_id 
                                 AND id = @curid);
        UPDATE coupon_operations SET balance = balance;
        SET i = i + 1;
      END;
    END WHILE;
  END IF;
END;
|

这是行不通的-我不知道如何通过居里。

解决方案是在准备好的语句本身中设置变量，如下所示：

SET @sql = CONCAT('SET @curid = SELECT id
                                FROM coupon_operations 
                                WHERE user_id = ? 
                                ORDER BY id ASC 
                                LIMIT ?, 1');

很高兴您找到答案。另一种解决方案是使用SELECT ... INTO语法：

SET @sql = CONCAT('SELECT id INTO @curid FROM coupon_operations 
                   WHERE user_id = ? 
                   ORDER BY id ASC 
                   LIMIT ?, 1');

请尝试这个。解决以下问题的Concatenate，PREPARE和EXECUTE语句。

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