查詢沒有子查詢？ SQL

Question

是否可以在沒有任何子查詢的情況下執行此查詢？或者更少的代碼？獲得相同的結果。

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，但一個DISTINCT關鍵字是必需的，以消除重複行。

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 

爲了進一步獲得更多的知識有關加入，請訪問以下鏈接：

• Visual Representation of SQL Joins

Answer 3

只要把你的tblc和tblb作爲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;