SQL - 僅當條件匹配時才選擇

Question

我有一張如下所示的表格。

ID NAME 
1 JOHN 
2 JANE 
3 JACK 

在一個簡單的select語句中，如何從表中查詢JOHN和JANE？

條件是：

i。結果必須返回JOHN和JANE。

ii。如果從表中刪除了JOHN或JANE，它只會返回空結果。

Answer 1

你可以使用GROUP BY/HAVING，確保有2場比賽：

SELECT Name 
FROM T 
WHERE Name IN ('JOHN', 'JANE') 
AND  EXISTS 
     ( SELECT 1 
      FROM T 
      WHERE Name IN ('JOHN', 'JANE') 
      HAVING COUNT(DISTINCT Name) = 2 
     ); 

或者你可以使用一個自聯接：

SELECT a.Name 
FROM T a 
     INNER JOIN T b 
      ON a.Name != b.Name 
WHERE a.Name IN ('JOHN', 'JANE') 
AND  b.Name IN ('JOHN', 'JANE'); 

Examples on SQL Fiddle (MySQL)

Examples on SQL Fiddle (Oracle)

Examples on SQL Fiddle (Postgresql)

Answer 2

試試這個：

SELECT 
    GROUP_CONCAT(`NAME`) as names 
FROM `TABLE` 
WHERE 1 
    AND NAME IN ('JOHN','JANE') 
HAVING names= 'JOHN,JANE' 

Answer 3

1. 創建函數JohnAndJaneBothExist()

2.

SELECT * FROM TABLENAME 
WHERE 
    JohnAndJaneBothExist and 
    Name In ('John', 'Jane')