Question

在PosgreSQL中，通常可以方便地创建“表格”，以便引用它们，例如。

with

selected_ids as (
select 1 as id
)

select *
from someTable
where id = (select id from selected_ids)

以这种方式提供id多个值是不可能的吗？我发现this answer建议使用values来解决类似问题，但我将其转换为以下示例时遇到问题。

我想写一些子查询，例如

select 1 as id
union
select 2 as id
union
select 7 as id

或

select 1 as id, 'dog' as animal
union
select 7 as id, 'cat' as animal

以更浓缩的方式，不重复自己。

Answer 1

你应该像这样使用union和IN语句：

with
selected_ids as (
select 1 as id
union
select 2 as id
union
select 3 as id
....
)
select *
from someTable
where id in (select id from selected_ids)

在审核wingedpanther's想法并寻找它之后，您可以使用他的想法，如果这些ID不断是这样的：

with
selected_ids as (
SELECT * FROM generate_series(Start,End) --(1,10) for example
)
select *
from someTable
where id in (select id from selected_ids)

如果它们不是连续的，那么你能做到这一点的唯一方法就是将这些ID存储在不同的表中（也许你已经拥有它，如果没有，也可以插入它）

然后：

select *
from someTable
where id in (select id from OtherTable)

Answer 2

您可以在查询别名中使用参数：

with selected_ids(id) as (
    values (1), (3), (5)
)
select *
from someTable
where id = any (select id from selected_ids)

您也可以使用join代替子查询，例如：

create table some_table (id int, str text);
insert into some_table values
(1, 'alfa'),
(2, 'beta'),
(3, 'gamma');

with selected_ids(id) as (
    values (1), (2)
)
select *
from some_table
join selected_ids
using(id);

 id | str  
----+------
  1 | alfa
  2 | beta
(2 rows)

Answer 3

您可以像这样

在WITH中传递id和animal字段

with selected_ids(id,animal) as (
values (1,'dog'), (2,'cat'), (3,'elephant'),(4,'rat')--,..,.. etc
)
select *
from someTable
where id = any (select id from selected_ids)

即时创建表

3 个答案: