问题
Possible Duplicate:
Function to Calculate Median in Sql Server
I have a table like this:
SET ANSI_NULLS ON
GO
SET QUOTED_IDENTIFIER ON
GO
SET ANSI_PADDING ON
GO
CREATE TABLE [dbo].[cars](
[id] [int] IDENTITY(1,1) NOT NULL,
[sp] [int] NOT NULL,
[dst] [int] NOT NULL,
[type] [varchar](10) NULL,
CONSTRAINT [PK_id] PRIMARY KEY CLUSTERED
(
[id] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
) ON [PRIMARY]
GO
SET ANSI_PADDING OFF
GO
SET IDENTITY_INSERT [dbo].[cars] ON
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (1, 4, 2, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (2, 4, 10, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (3, 7, 4, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (4, 7, 22, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (5, 8, 16, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (6, 9, 10, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (7, 10, 18, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (8, 10, 26, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (9, 10, 34, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (10, 11, 17, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (11, 11, 28, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (12, 12, 14, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (13, 12, 20, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (14, 12, 24, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (15, 12, 28, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (16, 13, 26, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (17, 13, 34, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (18, 13, 34, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (19, 13, 46, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (20, 14, 26, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (21, 14, 36, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (22, 14, 60, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (23, 14, 80, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (24, 15, 20, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (25, 15, 26, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (26, 15, 54, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (27, 16, 32, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (28, 16, 40, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (29, 17, 32, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (30, 17, 40, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (31, 17, 50, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (32, 18, 42, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (33, 18, 56, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (34, 18, 76, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (35, 18, 84, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (36, 19, 36, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (37, 19, 46, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (38, 19, 68, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (39, 20, 32, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (40, 20, 48, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (41, 20, 52, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (42, 20, 56, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (43, 20, 64, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (44, 22, 66, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (45, 23, 54, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (46, 24, 70, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (47, 24, 92, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (48, 24, 93, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (49, 24, 120, NULL)
INSERT [dbo].[cars] ([id], [sp], [dst], [type]) VALUES (50, 25, 85, NULL)
SET IDENTITY_INSERT [dbo].[cars] OFF
I can calculate agerage using group by clause
SELECT dst, AVG(sp) AS average
FROM dbo.cars
GROUP BY dbo.cars.dst
but I'm not able to find MEDIAN
function in SQLServer. How can I calculate median like this?
SELECT dst, MEDIAN(sp) AS median
FROM dbo.cars
GROUP BY dbo.cars.dst
回答1:
You need to change your code to use decimals as follows
SELECT
dst,
AVG(sp)
FROM
(
SELECT
dst,
cast(sp as decimal(5,2)) sp,
ROW_NUMBER() OVER (
PARTITION BY dst
ORDER BY sp ASC, id ASC) AS RowAsc,
ROW_NUMBER() OVER (
PARTITION BY dst
ORDER BY sp DESC, id DESC) AS RowDesc
FROM dbo.cars SOH
) x
WHERE
RowAsc IN (RowDesc, RowDesc - 1, RowDesc + 1)
GROUP BY dst
ORDER BY dst;
Currently, the AVG command is performed on an int, therefore the result is an int
回答2:
I think I found the solution, but this does not seem to produce even numbers (like 10.5)
SELECT
dst,
AVG(sp)
FROM
(
SELECT
dst,
sp,
ROW_NUMBER() OVER (
PARTITION BY dst
ORDER BY sp ASC, id ASC) AS RowAsc,
ROW_NUMBER() OVER (
PARTITION BY dst
ORDER BY sp DESC, id DESC) AS RowDesc
FROM dbo.cars SOH
) x
WHERE
RowAsc IN (RowDesc, RowDesc - 1, RowDesc + 1)
GROUP BY dst
ORDER BY dst;
回答3:
You can use partition by clause and ranking functions
来源:https://stackoverflow.com/questions/7091822/sql-server-how-to-calculate-median-group-by