Question

如何在MySQL查询中编写IF ELSE语句？

这样的事情：

mysql_query("...(irrelevant code).. IF(action==2&&state==0){state=1}");

然后在我的阵列中我应该能够做到这一点：

 $row['state'] 
//this should equal 1, the query should not change anything in the database, 
//just the variable for returning the information

Answer 1

您可能想要使用CASE expression。

他们看起来像这样：

SELECT col1, col2, (case when (action = 2 and state = 0) 
 THEN
      1 
 ELSE
      0 
 END)
 as state from tbl1;

Answer 2

你必须用SQL写它而不是C / PHP风格

IF( action = 2 AND state = 0, 1, 0 ) AS state

用于查询

IF ( action = 2 AND state = 0 ) THEN SET state = 1

用于存储过程或函数

Answer 3

您正在寻找case：

case when action = 2 and state = 0 then 1 else 0 end as state

MySQL有if语法（if(action=2 and state=0, 1, 0)），但case更通用。

请注意，as state只是对列进行别名。我假设这是在您的SQL查询的列列表中。

Answer 4

SELECT col1, col2, IF( action = 2 AND state = 0, 1, 0 ) AS state from tbl1;

OR

SELECT col1, col2, (case when (action = 2 and state = 0) then 1 else 0 end) as state from tbl1;

两个结果都一样....

Answer 5

根据mySQL参考手册，这是使用if和else语句的语法：

IF search_condition THEN statement_list
[ELSEIF search_condition THEN statement_list] ...
[ELSE statement_list]
END IF

关于您的查询：

x = IF((action=2)&&(state=0),1,2);

或者您可以使用

IF ((action=2)&&(state=0)) then 
state = 1;
ELSE 
state = 2;
END IF;