如何在PostgreSql中多次选择单行

Question

我想在PostgreSQL中打印同一行4次，如何实现呢？

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我想要像

这样的东西

Table : mytable

Id   |  name
------------
 1   |  foo
 2   |  bar
 3   |  zzz

结果应该是

Select 4x mytable.* from mytable where id=1

Answer 1

您可以与generate_series(1,4)交叉加入，这将返回包含数字1到4的表格：

SELECT mytable.*
FROM mytable 
CROSS JOIN generate_series(1,4) as x
WHERE id=1

对于原始结果集中的每一行，将有一个副本，旁边有1个，一个有2个，依此类推。

Answer 2

您可以使用generate_series。

<强>样品：

t=# create table so48 (i int,n text);
CREATE TABLE
t=# insert into so48 select 1,'a';
INSERT 0 1
t=# insert into so48 select 2,'b';
INSERT 0 1

选择

t=# with s as (select generate_series(1,4,1) g) select so48.* from so48 join s on true where i = 1;
 i | n
---+---
 1 | a
 1 | a
 1 | a
 1 | a
(4 rows)

Answer 3

使用union all

Select mytable.* from mytable where id=1
union all Select mytable.* from mytable where id=1
union all Select mytable.* from mytable where id=1
union all Select mytable.* from mytable where id=1

Answer 4

交叉联接应该完成这项工作

Select 4x mytable.* from mytable where id=1 
cross join
(select 1 from dual union all
select 1 from dual union all
select 1 from dual union all
select 1 from dual )