sql - MSSQL:使用 DISTINCT,没有 GROUP BY 子句的 TOP 选择
问题描述
我想使用没有 GROUP BY 子句的 DISTINCT 和 TOP 选择。
我想从 [locations] 中选择行并按与 [location_photos] 中的每个位置相关联的行数对结果进行排序
我现在有了这个(甚至不使用 TOP):
SELECT distinct(l.id),count(lp.locationid) OVER(partition by l.id) AS photos
,ISNULL(lp.locpath,'') as thumb
,l.id,l.title
FROM locations l
LEFT JOIN location_photos lp on lp.locationid=l.id
ORDER BY photos desc
然而,这会为 [location_photos] (56,000) 中的每一行返回一行,这应该是 [locations] (12,000) 中的潜在最大行数。
如何使用 DISTINCT 和 TOP 选择不同的行数?
DDL 和数据
CREATE TABLE [dbo].[locations](
[id] [int] NOT NULL,
[title] [nvarchar](500) NOT NULL,
[createdate] [datetime] NULL,
CONSTRAINT [PK_locs] PRIMARY KEY NONCLUSTERED
(
[id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, OPTIMIZE_FOR_SEQUENTIAL_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY] TEXTIMAGE_ON [PRIMARY]
GO
ALTER TABLE [dbo].[locations] ADD CONSTRAINT [DF_homes_createdate] DEFAULT (getdate()) FOR [createdate]
GO
CREATE TABLE [dbo].[location_photos](
[id] [int] IDENTITY(1,1) NOT NULL,
[locationid] [int] NOT NULL,
[locpath] [nvarchar](250) NOT NULL,
CONSTRAINT [PK_location_photos] PRIMARY KEY NONCLUSTERED
(
[id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON, OPTIMIZE_FOR_SEQUENTIAL_KEY = OFF) ON [PRIMARY]
) ON [PRIMARY]
GO
ALTER TABLE [dbo].[location_photos] WITH CHECK ADD CONSTRAINT [FK_locs_photos_homes] FOREIGN KEY([locationid])
REFERENCES [dbo].[locations] ([id])
ON DELETE CASCADE
GO
ALTER TABLE [dbo].[location_photos] CHECK CONSTRAINT [FK_locs_photos_homes]
GO
INSERT INTO [locations](id,title) VALUES (1,'new york')
INSERT INTO [locations](id,title) VALUES (2,'boston')
INSERT INTO [locations](id,title) VALUES (3,'chicago')
INSERT INTO [locations](id,title) VALUES (4,'los angeles')
INSERT INTO [location_photos](locationid,locpath) VALUES (1,'nyc1')
INSERT INTO [location_photos](locationid,locpath) VALUES (1,'nyc2')
INSERT INTO [location_photos](locationid,locpath) VALUES (1,'nyc3')
INSERT INTO [location_photos](locationid,locpath) VALUES (1,'nyc4')
INSERT INTO [location_photos](locationid,locpath) VALUES (1,'nyc5')
INSERT INTO [location_photos](locationid,locpath) VALUES (2,'boston1')
INSERT INTO [location_photos](locationid,locpath) VALUES (2,'boston2')
INSERT INTO [location_photos](locationid,locpath) VALUES (2,'boston3')
INSERT INTO [location_photos](locationid,locpath) VALUES (2,'boston4')
--there are not photos for chicago on purpose
INSERT INTO [location_photos](locationid,locpath) VALUES (4,'la1')
INSERT INTO [location_photos](locationid,locpath) VALUES (4,'la2')
解决方案
我想从 [locations] 中选择行并按与 [location_photos] 中的每个位置相关联的行数对结果进行排序
您可以在子句中使用相关子查询ORDER BY
:
select l.*
from locations l
order by (select count(*)
from location_photos lp
where lp.location_id = l.id
) desc;
如果您想要查询中的计数以及排序标准,只需将子查询移动到select
:
select l.*,
(select count(*)
from location_photos lp
where lp.location_id = l.id
) as num_photos
from locations l
order by num_photos desc;
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