有位朋友要求帮忙实现交叉表（将某些行变为列），之前虽然实现过，但没有整理，今天顺便整理一下，便于自己以后参考，希望对其他网友有帮助，欢迎指出不足之处^_^
数据库中原始数据类似：
要求前台显示为：
建立表结构：
CREATE TABLE [dbo].[t_Score] (
[ScoreId] [int] IDENTITY (1, 1) NOT NULL ,
[SubjectName] [varchar] (50) NOT NULL ,
[StudentName] [varchar] (10) NOT NULL ,
[ScoreValue] [real] NOT NULL ,
[ExamDate] [datetime] NOT NULL
)
样本数据
INSERT INTO t_Score(SubjectName, StudentName, ScoreValue, ExamDate)
VALUES('C语言', '孙光', 80, '2006-01-05')
INSERT INTO t_Score(SubjectName, StudentName, ScoreValue, ExamDate)
VALUES('日语', '孙光', 79, '2006-07-06')
INSERT INTO t_Score(SubjectName, StudentName, ScoreValue, ExamDate)
VALUES('C语言', '孙光', 89, '2006-08-09')
INSERT INTO t_Score(SubjectName, StudentName, ScoreValue, ExamDate)
VALUES('英语', '王二', 77, '2006-09-10')
INSERT INTO t_Score(SubjectName, StudentName, ScoreValue, ExamDate)
VALUES('英语', '孙光', 77, '2006-07-06')
INSERT INTO t_Score(SubjectName, StudentName, ScoreValue, ExamDate)
VALUES('C语言', '王二', 89, '2006-08-09')
1。通过存储过程实现
实现要点：
a. 使用一个临时表(#ScoreTbl)存储指定学生的所有成绩（根据实际情况，可能有更多条件）
说明：这里无法使用表变量，因为表变量无法用于动态SQL语句中。
b.临时表#ScoreTbl中使用一个平均值标志位，因为将每个科目的平均值计算出来之后也存入了#ScoreTbl
当然，根据需求，还可以增加总成绩标志位等等
c.使用递归的SELECT语句创建动态 DateExam（考试时间）列（参考：Paul Nielsen 的 Microsoft SQL Server 2000宝典 P353 12-7 递归的Select变量)
注意：这里递归成的 @sql 语句有个潜在的bug，就是@sql长度必须小于8000个字符（如果使用sq_executeSql执行动态语句，必须声名为nvarchar，则只能使用4000个字符）
邹建大哥的 化解字符串不能超过8000的方法及交叉表的处理 讨论了三种可选择的方案。
本示例不做此讨论，只求实现交叉表^_^
d.使用CASE表达式选择 DateExam 对应的 ScoreValue（成绩值）（参考：Paul Nielsen 的 Microsoft SQL Server 2000宝典 P353 12-7 -2 动态交叉表查询)
e.使用聚合函数（这里使用SUM）包含ScoreValue列，因为ScoreValue未出现在GROUP BY子句中
具体实现：
ALTER PROC usp_GetCrossScore4(
@StuName varchar(10)
)
AS
-- creates a temp table to hold the score records
CREATE TABLE #ScoreTbl(
ScoreId int,
SubjectName varchar(50),
StudentName varchar(10),
ScoreValue real,
ExamDate datetime,
AvgFlag bit DEFAULT(0) -- marks as the average of some subject
)
-- populates basic data of some student
INSERT INTO #ScoreTbl(ScoreId, SubjectName, StudentName, ScoreValue, ExamDate)
SELECT ScoreId, SubjectName, StudentName, ScoreValue, ExamDate FROM t_Score s WHERE s.StudentName = @StuName
-- calculates total for per subject and appends to the temp table
INSERT INTO #ScoreTbl(ScoreId, SubjectName, StudentName, ScoreValue, ExamDate, AvgFlag)
SELECT NULL, SubjectName, StudentName, AVG(ScoreValue), NULL, 1 FROM #ScoreTbl s GROUP BY SubjectName, StudentName
--SELECT * FROM #ScoreTbl
DECLARE @Sql varchar(8000)
-- NOTE: some known bug -> you make sure the length of the dynamical sql is less than 8000.
-- fortunately, Mr Zou have made a deep discussion againt it at http://blog.csdn.net/zjcxc/archive/2003/12/29/20075.aspx.
SET @Sql = 'SELECT SubjectName 科目'
SELECT @sql = @sql + ', SUM(CASE ExamDate WHEN ''' + CONVERT(varchar(20), ExamDate, 102) + ''' THEN ScoreValue ELSE NULL END)''' + CAST(YEAR(ExamDate) AS VARCHAR) + '年' + CAST(MONTH(ExamDate) AS VARCHAR) + '月' + CAST(DAY(ExamDate) AS VARCHAR) + '日'''
FROM (SELECT DISTINCT ExamDate FROM t_Score s WHERE s.StudentName = @StuName) ss
SET @Sql = @Sql + ', SUM(CASE AvgFlag WHEN 1 THEN ScoreValue ELSE NULL END) ''平均分'''
--PRINT @Sql
-- runs the dynamical sql statement
EXEC(@sql+' FROM #ScoreTbl s GROUP BY SubjectName')
ALTER PROC usp_GetCrossScore4(
@StuName varchar(10)
)
AS
-- creates a temp table to hold the score records
CREATE TABLE #ScoreTbl(
ScoreId int,
SubjectName varchar(50),
StudentName varchar(10),
ScoreValue real,
ExamDate datetime,
AvgFlag bit DEFAULT(0) -- marks as the average of some subject
)
-- populates basic data of some student
INSERT INTO #ScoreTbl(ScoreId, SubjectName, StudentName, ScoreValue, ExamDate)
SELECT ScoreId, SubjectName, StudentName, ScoreValue, ExamDate FROM t_Score s WHERE s.StudentName = @StuName
-- calculates total for per subject and appends to the temp table
INSERT INTO #ScoreTbl(ScoreId, SubjectName, StudentName, ScoreValue, ExamDate, AvgFlag)
SELECT NULL, SubjectName, StudentName, AVG(ScoreValue), NULL, 1 FROM #ScoreTbl s GROUP BY SubjectName, StudentName
--SELECT * FROM #ScoreTbl
DECLARE @Sql varchar(8000)
-- NOTE: some known bug -> you make sure the length of the dynamical sql is less than 8000.
-- fortunately, Mr Zou have made a deep discussion againt it at http://blog.csdn.net/zjcxc/archive/2003/12/29/20075.aspx.
SET @Sql = 'SELECT SubjectName 科目'
SELECT @sql = @sql + ', SUM(CASE ExamDate WHEN ''' + CONVERT(varchar(20), ExamDate, 102) + ''' THEN ScoreValue ELSE NULL END)''' + CAST(YEAR(ExamDate) AS VARCHAR) + '年' + CAST(MONTH(ExamDate) AS VARCHAR) + '月' + CAST(DAY(ExamDate) AS VARCHAR) + '日'''
FROM (SELECT DISTINCT ExamDate FROM t_Score s WHERE s.StudentName = @StuName) ss
SET @Sql = @Sql + ', SUM(CASE AvgFlag WHEN 1 THEN ScoreValue ELSE NULL END) ''平均分'''
--PRINT @Sql
-- runs the dynamical sql statement
EXEC(@sql+' FROM #ScoreTbl s GROUP BY SubjectName')
测试代码：
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效果：
源码：
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下篇介绍如何使用程序动态构造交叉表。
交叉表的简单实现2：使用前端程序实现