浅析SQL语句行列转换的两种方法 case...when与pivot函数的应用
SQL语句行列转换的两种方法 case...when和pivot函数应用，运用pivot 函数只支持数据库版本2005以上的。一般运用case when else end 的方法比较多，比较普遍
/*创建数据库*/ CREATE DATABASE tmp go USE tmp go/*创建数据库测试表*/CREATE TABLE [Scores] ( [ID] INT IDENTITY(1, 1) PRIMARY KEY , [Student] VARCHAR(20) , [Subject] VARCHAR(30) , [Score] FLOAT )goTRUNCATE TABLE Scores /*插入数据库测试数据信息*/ INSERT INTO Scores ( Student, Subject, Score ) VALUES ( 'test001', '语文', '90' ) INSERT INTO Scores ( Student, Subject, Score ) VALUES ( 'test001', '英语', '85' ) INSERT INTO Scores ( Student, Subject, Score ) VALUES ( 'text002', '语文', '90' ) INSERT INTO Scores ( Student, Subject, Score ) VALUES ( 'text002', '英语', '80' ) INSERT INTO Scores ( Student, Subject, Score ) VALUES ( 'test003', '语文', '95' ) INSERT INTO Scores ( Student, Subject, Score ) VALUES ( 'test003', '英语', '85' )/*1. case when .......then else ....end 用法，行列转换*/ SELECT Student AS '姓名' , MAX(CASE Subject WHEN '语文' THEN Score ELSE 0 END) AS '语文' ,--如果这个行是“语文”，就选此行作为列 MAX(CASE Subject WHEN '英语' THEN Score ELSE 0 END) AS '英语'FROM Scores GROUP BY Student ORDER BY Student/*2. pivot(聚合函数(要转成列值的列名) for 要转换的列 in（目标列名） )*/--by www.jbxue.comSELECT Student AS '姓名' , AVG(语文) AS '语文' , AVG(英语) AS '英语'FROM Scores PIVOT( AVG(Score) FOR Subject IN ( 语文, 英语 ) )as NewScores GROUP BY Student ORDER BY Student ASC
