SQL - 仅当条件匹配时才选择

Question

我有一张如下所示的表格。

ID NAME 
1 JOHN 
2 JANE 
3 JACK 

在一个简单的select语句中，如何从表中查询JOHN和JANE？

条件是：

i。结果必须返回JOHN和JANE。

ii。如果从表中删除了JOHN或JANE，它只会返回空结果。

Answer 1

你可以使用GROUP BY/HAVING，确保有2场比赛：

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 
     ); 

或者你可以使用一个自联接：

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

试试这个：

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

Answer 3

1. 创建函数JohnAndJaneBothExist()

2.

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