查询没有子查询？ SQL

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？获得相同的结果。

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

可以使用加入，但一个DISTINCT关键字是必需的，以消除重复行。

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 

为了进一步获得更多的知识有关加入，请访问以下链接：

• Visual Representation of SQL Joins

Answer 3

只要把你的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;