在mySQL中是否存在带有IF / ELSE语句的SELECT？

Question

Is it possible to have a SELECT statement in mySQL with an IF/ELSE clause in it?

Eg

I want to SELECT all table rows and return color2 ONLY if color2 is 'brown'. My example SQL select statement of what I would like to accomplish is below.

APPLES
+------+--------+----------+----------+  
|  ID  |  NAME  |  COLOR1  |  COLOR2  |  
+------+--------+----------+----------+  
|  1   | apple1 |    red   |   brown  |
+------+--------+----------+----------+  
|  2   | apple2 |    red   |   green  |
+------+--------+----------+----------+

SELECT name, (IF color2 = 'brown' SELECT color2 ELSE SELECT color1) AS color FROM apples

would return:

+----------+----------+
|  apple1  |   brown  |
+----------+----------+
|  apple2  |    red   |
+----------+----------+

Answer 1

MySQL有一个IF（）函数：

SELECT name, IF(color2='brown', color2, color1) AS color FROM apples

Answer 2

Use:

SELECT a.name, 
       CASE WHEN a.color2 = 'brown' THEN a.color2 ELSE a.color1 END AS color 
  FROM apples a

Reference: CASE

The CASE statement allows for IF/ELSE or SWITCH-like functionality, and has the benefit of being ANSI standard. That query would work on SQL Server, Oracle, MySQL...

Answer 3

查看MySQL参考手册中的CASE语句。

Answer 4

控制流功能文档应该可以帮助您。