Postgresql 单个语句中存在多个select
我有以下代码:Postgresql 单个语句中存在多个select,postgresql,select,multiple-columns,exists,Postgresql,Select,Multiple Columns,Exists,我有以下代码: 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)
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);
是否有一种方法可以检查单个语句中的多个条件
我在两个单独的列中查找值。
我想要的答案是这样的:
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)
演示:
演示:
那怎么办
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;
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;
EXISTS生成一个布尔值,您可以直接使用该值:
EXISTS生成一个布尔值,您可以直接使用该值:
这给了我一个专栏。我们的想法是使用多个这样的条件,并在一个查询中得到结果。我的错,我刚刚编辑了我的答案,但现在,我不确定您想做什么。如果您想检索两列数据,您可能应该在子查询之间使用一个
并集
。谢谢您的提示。我根据你的答案得到了解决方案。这给了我一列。我们的想法是使用多个这样的条件,并在一个查询中得到结果。我的错,我刚刚编辑了我的答案,但现在,我不确定您想做什么。如果您想检索两列数据,您可能应该在子查询之间使用一个并集
。谢谢您的提示。我根据你的答案得到了解决方案。
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;
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
;