在WHERE子句中进行Postgres数组查找

Question

我有一个问题:

SELECT bar, (SELECT name FROM names WHERE value = bar) as name
FROM foobar WHERE foo = 1 and bar = ANY (1,2,3)

我的问题是,当表中没有包含任何行bar = 3(或者请求的任何其他值)时foobar,不会为该值的bar返回任何行.

我希望我的查询返回一行[bar, NULL],但是想不出办法来解决这个问题.

这甚至可能吗？

Answer 1

也许这种方法就是你所追求的:

测试平台:

create view names as 
select 1 as value, 'Adam' as name union all select 2, 'Beth';

create view foobar as 
select 1 as foo, 1 as bar union all select 1, 2;

原方法:

select bar, (select name from names where value = bar) as name 
from foobar 
where foo = 1 and bar = any (array[1, 2, 3]);

 bar | name
-----+------
   1 | Adam
   2 | Beth
(2 rows)

替代方法:

with w as (select unnest(array[1, 2, 3]) as bar)
select bar, (select name from names where value = bar) as name
from w left outer join foobar using(bar);

 bar | name
-----+------
   1 | Adam
   2 | Beth
   3 |
(3 rows)

如果你在8.3或之前,没有内置unnest功能,但你可以自己动手(不是非常有效)替换:

create or replace function unnest(anyarray) returns setof anyelement as $$
  select $1[i] from generate_series(array_lower($1,1), array_upper($1,1)) i;
$$ language 'sql' immutable;