查询子查询

Question

我试图做这样的事情：

SELECT t1.*, 
     t2.* 
FROM (SELECT * 
     FROM USER) AS t1, 
     (SELECT * 
     FROM t1) AS t2 

它不会在MySQL的工作。是否像上述可能？我的另一种选择是采取最后的子查询，并围绕主查询“换行”。想法？

Answer 1

用途：

SELECT t1.*, 
     t2.* 
    FROM (SELECT * 
      FROM USER) AS t1, 
     (SELECT * 
      FROM (SELECT * 
        FROM USER) AS t1) AS t2 

的WITH语法允许你建立在热膨胀系数的顶部：

WITH t1 AS (
    SELECT * FROM USER), -- comma separates them 
    t2 AS (
    SELECT * FROM t1) 
SELECT t1.*, t2.* 
    FROM t1, t2 

..但MySQL不支持WITH子句。

Answer 2

为什么不

SELECT t1.*, t2.* FROM USER as t1, USER as t2 

？你还应该添加一个条件，否则这将会产生大量的行。

现在，如果你的意思是问怎么来指代前面的子查询，你应该重复它，并添加所需的额外条件：

SELECT t1.*, t2.* FROM (SELECT bar FROM foo WHERE baz=1) as t1, 
(SELECT bluz,bar FROM foo WHERE baz=1 AND quux = 0) as t2 WHERE t2.bar = t1.bar 

另一种选择是创建一个子查询视图或临时表（t1）

Answer 3

如果2个表的列数相同，则可以使用例如UNION 例如

SELECT * 
FROM USER 
UNION 
SELECT * 
FROM t1 

如果它们不具有相同的列，那么您将需要使用某种方式来加入表，如使用外键。例如。

SELECT * 
FROM USER as t1 
JOIN t1 as t2 (on t1.id = t2.id) 

Answer 4

我假设你的实际查询要复杂得多。是否有可能你可以创建一个视图来表示你的子查询，然后你可以使用一个更简单的选择语句，比如Vinko Vrsalovic建议的。