mysql使用查询结果作为临时表

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（一）select查询作为临时表

select cou,name from (select count(*) AS cou,enabled AS name from `user` group by enabled ) as a where cou>0

上面的语句就是将查询结果作为临时表，然后再在这个临时表中查找满足条件的数据。

语法: （注意：AS 可省略）

CODE: SELECT ... FROM (subquery) AS tableName ...

先创建一个表:

CODE: CREATE TABLE t1 (s1 INT, s2 CHAR(5), s3 FLOAT);
INSERT INTO t1 VALUES (1,'1',1.0);
INSERT INTO t1 VALUES (2,'2',2.0);

我们就可以进行以下的嵌套查询了:

  CODE: SELECT sb1,sb2,sb3
   FROM (SELECT s1 AS sb1, s2 AS sb2, s3*2 AS sb3 FROM t1) AS sb
   WHERE sb1 > 1;

结果是： 2, '2', 4.0.

SELECT AVG(sum_column1)
FROM (SELECT SUM(column1) AS sum_column1
FROM t1 GROUP BY column1) AS t1;

（二）行的子查询（Row Subquery）

SELECT * FROM t1 WHERE ROW(1,2) = (SELECT column1, column2 FROM t2);

在该例子中，在保证子查询返回单一行数据的前提下，如果 column1=1 且 column2=2 ，则该查询结果为 TRUE。

MySQL 行构造符

在上面的例子中，WHERE 后面的 (1,2) 被称为行构造符，也可以写作 ROW(1，2)。行构造符通常用于与对能返回两个或两个以上列的子查询进行比较。

SELECT * FROM article WHERE (title,content,uid) = (SELECT title,content,uid FROM blog WHERE bid=2)注意：[SQL] SELECT * FROM `user` WHERE ROW(username,`password`) = (SELECT username, `password` FROM `user`);[Err] 1242 - Subquery returns more than 1 row这是因为查询结果多于一行，可以这样处理SELECT * FROM `user` WHERE ROW(username,`password`) = ANY(SELECT username, `password` FROM `user`);

（三）.使用Exist和Not Exist参数

SELECT <span style="color:#ff0000;">DISTINCT</span> store_type FROM Stores                    WHERE <span style="color:#ff0000;">EXISTS</span> (SELECT * FROM Cities_Stores                                  WHERE Cities_Stores.store_type = Stores.store_type);

SELECT DISTINCT store_type FROM Stores                       WHERE <span style="color:#cc0000;">NOT EXISTS</span> (SELECT * FROM Cities_Stores                                   WHERE Cities_Stores.store_type = Stores.store_type);

（四）条件关联关系查询

SELECT column1 FROM t1 AS x     WHERE x.column1 = (SELECT column1 FROM t2 AS x          WHERE x.column1 = (SELECT column1 FROM t3               WHERE x.column2 = t3.column1));    跟其他数据库做法是一样的。

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