单个语句中存在多个 select

Question

我有如下一段代码：

DROP SCHEMA IF EXISTS s CASCADE;  

CREATE SCHEMA s;

CREATE TABLE s.t1 (
    id1 BigInt,
    id2 BigInt,
    CONSTRAINT "pk1" PRIMARY KEY (id1)
)   
WITH(OIDS=FALSE);


INSERT INTO s.t1 (id1, id2) VALUES (2, 22);
INSERT INTO s.t1 (id1, id2) VALUES (3, 22);
INSERT INTO s.t1 (id1, id2) VALUES (4, 24);


SELECT EXISTS (SELECT TRUE FROM s.t1 t1 WHERE t1.id1 = 2,  
SELECT EXISTS (SELECT TRUE FROM s.t1 t1 WHERE t1.id2 = 22);

有没有办法在一条语句中检查多个条件。

我在两个单独的列中查找值。我正在寻找的答案是这样的：

 bool | bool 
------+------
 t    | t
(1 row)

我得到了解决方案：

SELECT EXISTS(SELECT TRUE FROM s.t1 t1 WHERE t1.id1 = 6), 
EXISTS(SELECT TRUE FROM s.t1 t1 WHERE t1.id2 = 22);

输出：

 exists | exists 
 --------+--------
  f      | t
 (1 row)

Answer 1

SELECT max( case when id1=2 then 'EXISTS' ELSE 'DOESN''T EXISTS' end) id1_2,
       max( case when id2=22 then 'EXISTS' ELSE 'DOESN''T EXISTS' end) id2_22,
       max( case when id2=33 then 'EXISTS' ELSE 'DOESN''T EXISTS' end) id2_33
FROM s.t1

演示：http://sqlfiddle.com/#!17/85c47/11

|  id1_2 | id2_22 |         id2_33 |
|--------|--------|----------------|
| EXISTS | EXISTS | DOESN'T EXISTS |

Answer 2

怎么样

SELECT max(x.t2) as t2,
       max(x.t22) as t22
FROM ((SELECT t1.id1 as t2, null as t22 FROM s.t1 t1 WHERE t1.id1 = 2)
        UNION
      (SELECT null as t2, t1.id2 as t22 FROM s.t1 t1 WHERE t1.id2 = 22)) as x;

Demo

Answer 3

EXISTS 产生一个布尔值，可以直接使用：

SELECT
  EXISTS (SELECT * FROM s.t1 x1  
        WHERE x1.id1 = 2)       AS ex1
  , EXISTS (SELECT * FROM s.t1 x2
        WHERE x2.id2 = 22)      AS ex2
        ;

单个语句中存在多个 select

Multiple select exists in a single statement

postgresql

select

multiple-columns

exists