MySQL - 在重复键上 - CASE WHEN THEN ELSE 不起作用

Question

我想在数据库中插入一个条目（uid、A、B）。如果条目已经存在，我将使用条件更新“A”和“B”列： （1 = 旧条目；[2] = 新条目）

A = (B[1] == B[2]) ? A[1] : A[2];
B = B[2] + 1;

我的查询：

INSERT INTO TableName (uid,A,B) 
VALUES (uid,A[2],B[2]) 
ON DUPLICATE KEY 
UPDATE  A= (SELECT CASE B WHEN B[2] THEN A ELSE A[2] END), 
        B= B[2]+1;

Ex1：

Old entry : uid = 1; A = 2; B = 4;
New entry : uid = 1; A = 3; B = 4;
-> Should be: A = 2; B = 5;
But my result: A = 3; B = 5; -> FAIL

Ex2：

Old entry : uid = 1; A = 2; B = 4;
New entry : uid = 1; A = 3; B = 6;
-> A = 3; B = 7; (my code works well in this ex) -> OK

非常感谢。

答案 1：删除 SELECT 键使其工作

INSERT INTO TableName (uid,A,B) 
VALUES (uid,A[2],B[2]) 
ON DUPLICATE KEY 
UPDATE  A= (CASE B WHEN B[2] THEN A ELSE A[2] END), 
        B= B[2]+1;

p-jairaj的答案

INSERT INTO TableName (uid,A,B) 
VALUES (uid,A[2],B[2]) 
ON DUPLICATE KEY 
UPDATE  A= (IF(B=B[2],A,A[2])), 
        B= B[2]+1;

Answer 1

试试这个：

INSERT INTO TableName (uid,A,B) 
VALUES (uid,A[2],B[2]) 
ON DUPLICATE KEY 
UPDATE  A= (IF(B=B[2],A,A[2])), 
        B= B[2]+1;