(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) AStableName …

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 DISTINCT store_type FROM Stores

WHERE EXISTS (SELECT * FROM Cities_Stores

WHERE Cities_Stores.store_type = Stores.store_type);

SELECT DISTINCT store_type FROM Stores

WHERE NOT EXISTS (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。