SQL行转列和列转行代码详解

行列互转，是一个经常遇到的需求。实现的方法，有case when方式和2005之后的内置pivot和unpivot方法来实现。
在读了技术内幕那一节后，虽说这些解决方案早就用过了，却没有系统性的认识和总结过。为了加深认识，再总结一次。
行列互转，可以分为静态互转，即事先就知道要处理多少行（列）;动态互转,事先不知道处理多少行(列)。

--创建测试环境
USE tempdb;
GO
IF OBJECT_ID('dbo.Orders') IS NOT NULL
 DROP TABLE dbo.Orders;
GO
CREATE TABLE dbo.Orders
(
 orderid  int    NOT NULL PRIMARY KEY NONCLUSTERED,
 orderdate datetime  NOT NULL,
 empid   int    NOT NULL,
 custid  varchar(5) NOT NULL,
 qty    int    NOT NULL
);
CREATE UNIQUE CLUSTERED INDEX idx_orderdate_orderid
 ON dbo.Orders(orderdate, orderid);
INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty)
 VALUES(30001, '20020802', 3, 'A', 10);
INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty)
 VALUES(10001, '20021224', 1, 'A', 12);
INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty)
 VALUES(10005, '20021224', 1, 'B', 20);
INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty)
 VALUES(40001, '20030109', 4, 'A', 40);
INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty)
 VALUES(10006, '20030118', 1, 'C', 14);
INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty)
 VALUES(20001, '20030212', 2, 'B', 12);
INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty)
 VALUES(40005, '20040212', 4, 'A', 10);
INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty)
 VALUES(20002, '20040216', 2, 'C', 20);
INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty)
 VALUES(30003, '20040418', 3, 'B', 15);
INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty)
 VALUES(30004, '20020418', 3, 'C', 22);
INSERT INTO dbo.Orders(orderid, orderdate, empid, custid, qty)
 VALUES(30007, '20020907', 3, 'D', 30);
GO 

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