MySQL触发器 - 将SELECT存储在变量中

Question

我有一个触发器,我希望有一个变量,它保存一个INT SELECT,我可以在两个IF语句中使用它,而不是调用SELECT两次.如何在MySQL触发器中声明/使用变量？

Answer 1

您可以使用DECLARE语法在MySQL触发器中声明局部变量.

这是一个例子:

DROP TABLE IF EXISTS foo;
CREATE TABLE FOO (
  i SERIAL PRIMARY KEY
);

DELIMITER //
DROP TRIGGER IF EXISTS bar //

CREATE TRIGGER bar AFTER INSERT ON foo
FOR EACH ROW BEGIN
  DECLARE x INT;
  SET x = NEW.i;
  SET @a = x; -- set user variable outside trigger
END//

DELIMITER ;

SET @a = 0;

SELECT @a; -- returns 0

INSERT INTO foo () VALUES ();

SELECT @a; -- returns 1, the value it got during the trigger

为变量赋值时,必须确保查询仅返回单个值,而不是一组行或一组列.例如,如果您的查询在实践中返回单个值,则可以,但只要它返回多行,就会得到" ERROR 1242: Subquery returns more than 1 row".

您可以使用LIMIT或MAX()确保将局部变量设置为单个值.

CREATE TRIGGER bar AFTER INSERT ON foo
FOR EACH ROW BEGIN
  DECLARE x INT;
  SET x = (SELECT age FROM users WHERE name = 'Bill'); 
  -- ERROR 1242 if more than one row with 'Bill'
END//

CREATE TRIGGER bar AFTER INSERT ON foo
FOR EACH ROW BEGIN
  DECLARE x INT;
  SET x = (SELECT MAX(age) FROM users WHERE name = 'Bill');
  -- OK even when more than one row with 'Bill'
END//

Answer 2

`CREATE TRIGGER `category_before_ins_tr` BEFORE INSERT ON `category`
  FOR EACH ROW
BEGIN
    **SET @tableId= (SELECT id FROM dummy LIMIT 1);**

END;`;

Answer 3

CREATE TRIGGER clearcamcdr AFTER INSERT ON `asteriskcdrdb`.`cdr` 
FOR EACH ROW
BEGIN
  SET @INC = (SELECT sip_inc FROM trunks LIMIT 1);
  IF NEW.billsec >1 AND NEW.channel LIKE @INC 
    AND NEW.dstchannel NOT LIKE "" 
  THEN
    insert into `asteriskcdrdb`.`filtre` (id_appel,date_appel,source,destinataire,duree,sens,commentaire,suivi) 
      values (NEW.id,NEW.calldate,NEW.src,NEW.dstchannel,NEW.billsec,"entrant","",""); 
  END IF;
END$$

别试试@ home

Answer 4

我发布这个解决方案是因为我很难找到我需要的东西。这篇文章让我足够接近（+1谢谢），这是如果数据与 test 匹配则在插入之前重新排列列数据的最终解决方案。

注意：这是来自我继承的遗留项目，其中：

1. rridprefix唯一密钥是+的组合rrid
2. 在我接手之前，没有任何限制可以防止重复的唯一键
3. 我们需要将两个表（其中一个充满重复项）合并到主表中，主表现在对组合键有约束（因此合并失败，因为获取表不允许来自不干净表的重复项）
4. on duplicate key不太理想，因为列太多并且可能会发生变化

无论如何，这里的触发器将任何重复的键放入旧列中，同时允许我们存储旧的错误数据（并且不会触发获取表复合的唯一键）。

BEGIN
  -- prevent duplicate composite keys when merging in archive to main
  SET @EXIST_COMPOSITE_KEY = (SELECT count(*) FROM patientrecords where rridprefix = NEW.rridprefix and rrid = NEW.rrid);

  -- if the composite key to be introduced during merge exists, rearrange the data for insert
  IF @EXIST_COMPOSITE_KEY > 0
  THEN

    -- set the incoming column data this way (if composite key exists)

    -- the legacy duplicate rrid field will help us keep the bad data
    SET NEW.legacyduperrid = NEW.rrid;

    -- allow the following block to set the new rrid appropriately
    SET NEW.rrid = null;

  END IF;

  -- legacy code tried set the rrid (race condition), now the db does it
  SET NEW.rrid = (
    SELECT if(NEW.rrid is null and NEW.legacyduperrid is null, IFNULL(MAX(rrid), 0) + 1, NEW.rrid)
    FROM patientrecords
    WHERE rridprefix  = NEW.rridprefix
  );
END