mySQL- Trigger更新COUNT基本插入值

Question

我想为mySQL创建一个触发器

1. 将数据插入my table A(id, i_Year=2017, i_Number=NULL)

后触发

2. 从表A中得到一个伯爵B：基本计算insert(New.i_Year)

3. 将count-B更新为表A中的i_Number

   DELIMITER $$
   CREATE TRIGGER  update_1
   AFTER INSERT ON TABLEA
   FOR EACH ROW
   BEGIN
   
   UPDATE TABLEA
   SET TABLEA.i_Number = (SELECT COUNT(*)+1 FROM TABLEA WHERE TABLEA.i_Year = New.i_Year)
   FROM TABLEA 
   WHERE TABLEA.id = New.id;
   
   END$$
   DELIMITER ;
   

有人可以帮我吗？

Answer 1

您可以将触发器更改为BEFORE INSERT并设置新行的计数，例如：

DELIMITER $$
CREATE TRIGGER  update_1
BEFORE INSERT ON TABLEA
FOR EACH ROW
BEGIN
DECLARE row_count int;

SELECT COUNT(*)+1 INTO row_count FROM TABLEA WHERE TABLEA.i_Year = New.i_Year
SET NEW.i_Number = row_count;

END$$
DELIMITER ;