Question

我有一个查询，我想在同一表上用all all聚合多个子查询的结果，并且只返回有限数量的记录。

子查询1：

SELECT "bookings".* FROM "bookings"
WHERE "bookings"."guest_id" = 19317644 
    AND "bookings"."status" IN (0)
    AND (created_at > '2017-10-04 05:27:29.740508')
ORDER BY "bookings"."id" ASC LIMIT 1;

子查询2：

SELECT "bookings".* FROM "bookings"
WHERE "bookings"."guest_id" = 19317644 
    AND "bookings"."status" IN (1)
    AND (created_at > '2017-10-04 05:27:29.740508')
ORDER BY "bookings"."id" ASC LIMIT 1;

我想从两个查询的结果中总共显示一条记录。

Answer 1

您可以使用结果集中的列号对UNION的结果进行排序。因此，如果“ id”是“ select * from bookings”返回的第一列，则可以执行以下操作：

SELECT "bookings".* FROM "bookings"
WHERE "bookings"."guest_id" = 19317644 
    AND "bookings"."status" IN (0)
    AND (created_at > '2017-10-04 05:27:29.740508')

UNION ALL

SELECT "bookings".* FROM "bookings"
WHERE "bookings"."guest_id" = 19317644 
    AND "bookings"."status" IN (1)
    AND (created_at > '2017-10-04 05:27:29.740508')

ORDER BY 1

关于LIMIT，我不清楚您要做什么：仅显示每个查询中的一条记录，或显示两个查询结果中的一条记录。

最后，我不确定在生成示例时是否丢失了一些细节，但这可能更简单：

SELECT "bookings".* FROM "bookings"
WHERE "bookings"."guest_id" = 19317644 
    AND "bookings"."status" IN (0,1)
    AND (created_at > '2017-10-04 05:27:29.740508')

更新：

如果要显示一条记录总数，则只需在语句末尾添加LIMIT子句即可。例如：

create table foo (a int);
insert into foo (a) values (1);
create table bar (b int);
insert into bar (b) values (2);

select * from foo
union all
select * from bar
order by 1
limit 1

Answer 2

使用CTE合并数据

    WITH client_1 AS (
    SELECT "bookings".* FROM "bookings"
    WHERE "bookings"."guest_id" = 19317644 
        AND "bookings"."status" IN (0)
        AND (created_at > '2017-10-04 05:27:29.740508')
    ORDER BY "bookings"."id" ASC LIMIT 1
    ), client_2 AS (
    SELECT "bookings".* FROM "bookings"
    WHERE "bookings"."guest_id" = 19317644 
        AND "bookings"."status" IN (1)
        AND (created_at > '2017-10-04 05:27:29.740508')
    ORDER BY "bookings"."id" ASC LIMIT 1
    ), consolidated AS (
SELECT * FROM client_1 UNION ALL SELECT * FROM CLIENT_2
)
SELECT * FROM CONSOLIDATED;

，然后排序，限制或在哪里仅使用“合并”表，它将具有来自两个查询的数据

如何在PostgreSQL中使用Order by子句并限制所有并集？

2 个答案: