你可以有，如果

2018-07-03 20:46:32

这个问题在这里已经有了答案：

如何在SQL SELECT中执行IF ... THEN？ 22个答案

您可以进行以下sql查询

IF ((SELECT COUNT(*) FROM table1 WHERE project = 1) > 0) 
    SELECT product, price FROM table1 WHERE project = 1
ELSE IF ((SELECT COUNT(*) FROM table1 WHERE project = 2) > 0) 
    SELECT product, price FROM table1 WHERE project = 2
ELSE IF ((SELECT COUNT(*) FROM table1 WHERE project = 3) > 0)
    SELECT product, price FROM table1 WHERE project = 3

CASE语句最接近SQL中的IF语句，并且在所有版本的SQL Server上都受支持：

SELECT CASE <variable> 
           WHEN <value>      THEN <returnvalue> 
           WHEN <othervalue> THEN <returnthis> 
           ELSE <returndefaultcase> 
       END 
  FROM <table>

而不是使用EXISTS和COUNT只需使用@@ROWCOUNT ：

select product, price from table1 where project = 1

IF @@ROWCOUNT = 0
BEGIN
    select product, price from table1 where customer = 2

    IF @@ROWCOUNT = 0
    select product, price from table1 where company = 3
END

链接地址: http://www.djcxy.com/p/94335.html

上一篇: Can you have if

下一篇: MySQL select from subquery order