如何在 MySQL 查询中编写 IF ELSE 语句
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How do write IF ELSE statement in a MySQL query
提问by Dylan Cross
How do I write an IF ELSE statement in a MySQL query?
如何在 MySQL 查询中编写 IF ELSE 语句？
Something like this:
像这样的东西：
mysql_query("...(irrelevant code).. IF(action==2&&state==0){state=1}");
Then down in my array I should be able to do this:
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
回答by Hyman Edmonds
You probably want to use a CASEexpression.
您可能想要使用CASE表达式。
They look like this:
它们看起来像这样：
SELECT col1, col2, (case when (action = 2 and state = 0)
THEN
1
ELSE
0
END)
as state from tbl1;
回答by SergeS
you must write it in SQL not it C/PHP style
你必须用 SQL 写它而不是 C/PHP 风格
IF( action = 2 AND state = 0, 1, 0 ) AS state
for use in query
用于查询
IF ( action = 2 AND state = 0 ) THEN SET state = 1
for use in stored procedures or functions
用于存储过程或函数
回答by Eric
You're looking for case:
您正在寻找case：
case when action = 2 and state = 0 then 1 else 0 end as state
MySQL has an ifsyntax (if(action=2 and state=0, 1, 0)), but caseis more universal.
MySQL 有一个if语法 ( if(action=2 and state=0, 1, 0))，但case更通用。
Note that the as statethere is just aliasing the column. I'm assuming this is in the column list of your SQL query.
请注意，as state该列只是别名。我假设这是在您的 SQL 查询的列列表中。
回答by Khandad Niazi
SELECT col1, col2, IF( action = 2 AND state = 0, 1, 0 ) AS state from tbl1;
OR
或者
SELECT col1, col2, (case when (action = 2 and state = 0) then 1 else 0 end) as state from tbl1;
both results will same....
两个结果都一样....
回答by Dilraj Singh
according to the mySQL reference manual this the syntax of using if and else statement :
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
IF search_condition THEN statement_list [ELSEIF search_condition THEN statement_list] ... [ELSE statement_list] END IF
So regarding your query :
所以关于你的查询：
x = IF((action=2)&&(state=0),1,2);
or you can use
或者你可以使用
IF ((action=2)&&(state=0)) then
state = 1;
ELSE
state = 2;
END IF;
There is good example in this link : http://easysolutionweb.com/sql-pl-sql/how-to-use-if-and-else-in-mysql/
这个链接中有一个很好的例子：http: //easysolutionweb.com/sql-pl-sql/how-to-use-if-and-else-in-mysql/
