统计学生各科成绩，列转行

----查询学生各科成绩报表，一步一步分析

学生表

USE [Test]
GO

/****** Object:  Table [dbo].[student]    Script Date: 2017/7/10 12:17:00 ******/
SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

SET ANSI_PADDING ON
GO

CREATE TABLE [dbo].[student](
[stuId] [NVARCHAR](50) NOT NULL,
[stuName] [VARCHAR](10) NOT NULL,
[stuSex] [CHAR](2) NULL,
[age] [INT] NULL,
CONSTRAINT [PK__student__AEC9BF8FBC61E94F] PRIMARY KEY CLUSTERED
(
[stuId] 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

ALTER TABLE [dbo].[student]  WITH CHECK ADD  CONSTRAINT [CK__student__age__117F9D94] CHECK  (([age]>=(15) AND [age]<=(45)))
GO

ALTER TABLE [dbo].[student] CHECK CONSTRAINT [CK__student__age__117F9D94]
GO

ALTER TABLE [dbo].[student]  WITH CHECK ADD  CONSTRAINT [CK__student__age__1920BF5C] CHECK  (([age]>=(15) AND [age]<=(45)))
GO

ALTER TABLE [dbo].[student] CHECK CONSTRAINT [CK__student__age__1920BF5C]
GO

ALTER TABLE [dbo].[student]  WITH CHECK ADD  CONSTRAINT [CK__student__stuSex__108B795B] CHECK  (([stuSex]='男' OR [stuSex]='女'))
GO

ALTER TABLE [dbo].[student] CHECK CONSTRAINT [CK__student__stuSex__108B795B]
GO

ALTER TABLE [dbo].[student]  WITH CHECK ADD  CONSTRAINT [CK__student__stuSex__1A14E395] CHECK  (([stuSex]='男' OR [stuSex]='女'))
GO

ALTER TABLE [dbo].[student] CHECK CONSTRAINT [CK__student__stuSex__1A14E395]
GO

科目表

USE [Test]
GO

/****** Object:  Table [dbo].[course]    Script Date: 2017/7/10 12:17:54 ******/
SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

SET ANSI_PADDING ON
GO

CREATE TABLE [dbo].[course](
[couId] [NVARCHAR](50) NOT NULL,
[couName] [VARCHAR](20) NOT NULL,
CONSTRAINT [PK__course__965389F7BE4EE6DC] PRIMARY KEY CLUSTERED
(
[couId] 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

成绩表

USE [Test]
GO

/****** Object:  Table [dbo].[score]    Script Date: 2017/7/10 12:19:34 ******/
SET ANSI_NULLS ON
GO

SET QUOTED_IDENTIFIER ON
GO

CREATE TABLE [dbo].[score](
[stuId] [NVARCHAR](50) NOT NULL,
[couId] [NVARCHAR](50) NOT NULL,
[grade] [INT] NULL,
CONSTRAINT [PK__score__C7AC871022E01D82] PRIMARY KEY CLUSTERED
(
[stuId] ASC,
[couId] 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

ALTER TABLE [dbo].[score]  WITH CHECK ADD  CONSTRAINT [fk_couId] FOREIGN KEY([couId])
REFERENCES [dbo].[course] ([couId])
GO

ALTER TABLE [dbo].[score] CHECK CONSTRAINT [fk_couId]
GO

ALTER TABLE [dbo].[score]  WITH CHECK ADD  CONSTRAINT [fk_stuId] FOREIGN KEY([stuId])
REFERENCES [dbo].[student] ([stuId])
GO

ALTER TABLE [dbo].[score] CHECK CONSTRAINT [fk_stuId]
GO

ALTER TABLE [dbo].[score]  WITH CHECK ADD  CONSTRAINT [CK__score__grade__164452B1] CHECK  (([grade]>=(0) AND [grade]<=(100)))
GO

ALTER TABLE [dbo].[score] CHECK CONSTRAINT [CK__score__grade__164452B1]
GO

----1.查询所有学生信息以及各科成绩集合

SELECT s.*,c.grade,r.couName FROM dbo.student AS s

LEFT JOIN dbo.score AS c ON c.stuId=s.stuId

LEFT JOIN dbo.course AS r ON c.couId=r.couId

----2.将各科成绩转换成一行

SELECT s.stuId,s.stuName,s.stuSex,s.age,

CASE r.couName WHEN '数学' THEN  c.grade  ELSE 0 END AS '数学',

CASE r.couName WHEN '语文' THEN  c.grade  ELSE 0 END AS '语文',

CASE r.couName WHEN '英语' THEN  c.grade  ELSE 0 END AS '英语',

CASE r.couName WHEN '历史' THEN  c.grade  ELSE 0 END AS '历史'

 FROM dbo.student AS s

LEFT JOIN dbo.score AS c ON c.stuId=s.stuId

LEFT JOIN dbo.course AS r ON c.couId=r.couId

----3.统计成绩总数，并分组

SELECT s.stuId,s.stuName,

SUM(CASE r.couName WHEN '数学' THEN  c.grade  ELSE 0 END) AS '数学',

SUM(CASE r.couName WHEN '语文' THEN  c.grade  ELSE 0 END) AS '语文',

SUM(CASE r.couName WHEN '英语' THEN  c.grade  ELSE 0 END) AS '英语',

SUM(CASE r.couName WHEN '历史' THEN  c.grade  ELSE 0 END) AS '历史'

 FROM dbo.student AS s

LEFT JOIN dbo.score AS c ON c.stuId=s.stuId

LEFT JOIN dbo.course AS r ON c.couId=r.couId

GROUP BY s.stuId,s.stuName

----4.或max（）者也可以

SELECT s.stuId,s.stuName,

max(CASE r.couName WHEN '数学' THEN  c.grade  ELSE 0 END) AS '数学',

max(CASE r.couName WHEN '语文' THEN  c.grade  ELSE 0 END) AS '语文',

max(CASE r.couName WHEN '英语' THEN  c.grade  ELSE 0 END) AS '英语',

max(CASE r.couName WHEN '历史' THEN  c.grade  ELSE 0 END) AS '历史'

 FROM dbo.student AS s

LEFT JOIN dbo.score AS c ON c.stuId=s.stuId

LEFT JOIN dbo.course AS r ON c.couId=r.couId

GROUP BY s.stuId,s.stuName