Question

是否可以在没有任何子查询的情况下执行此查询？或者更少的代码？得到相同的结果。

SELECT person 
FROM tbla 
WHERE person IN 
(SELECT person 
FROM tblb 
WHERE age IN 
(SELECT age 
FROM tblc 
where age = '20'));

Answer 1

SELECT tbla.person 
FROM tbla 
inner join tblb on tblb.person = tbla.person
inner join tblc on tblc.age = tblb.age
WHERE tblc.age = '20'

Answer 2

您可以使用加入，但需要使用DISTINCT关键字来消除重复的行。

SELECT  DISTINCT a.*
FROM    tbla a
        INNER JOIN tblb b
            ON a.person = b.person
        INNER JOIN tblc c
            ON b.age = c.age
WHERE   c.age = 20

要进一步了解联接，请访问以下链接：

Visual Representation of SQL Joins

Answer 3

只需将tblc和tblb作为INNER JOIN：

SELECT tbla.person 
FROM tbla 
INNER JOIN tblb 
  ON tblb.person = tbla.person 
INNER JOIN tblc 
  ON tblc.age = tblb.age 
WHERE tblc.age = 20;

没有子查询的查询？ SQL

3 个答案: