子查詢與多個SELECT語句

Question

檢查其內的多個選擇語句子查詢「不」條件

EG。

select id from tbl where 
id not in (select id from table1) and 
id not in (select id from table2) and 
id not in (select id from table3) 

，而不是重複「不」條件相同的id，我需要將一次性檢查多個表的子查詢..

請幫助..

Answer 1

你可以使用一個工會，所以你只要有一個in：

select id 
from tbl 
where id not in 
     (
     select id from table1 
     union all select id from table2 
     union all select id from table3 
     ) 

注意：not in不適用於可爲空的列，但我認爲id在此處不可空。

Answer 2

您所查詢的是更好表現爲：

SELECT id 
FROM tbl t 
LEFT JOIN table1 t1 on t1.id = t.id 
LEFT JOIN table2 t2 on t2.id = t.id 
LEFT JOIN table3 t3 on t3.id = t.id 
WHERE t1.id IS NULL AND t2.id IS NULL AND t3.id IS NULL