对于自定义分组,一向是比较烦琐的,幸好sqlServer2005提供了FOR XML PATH的语法能够很方便的解决该问题,同时采用自定义函数的方式还能够更方便的进行扩展;Oracle10g以后提供了一个wmsys.wm_concat函数,也可以起到类似的作用。
下面以sqlServer2005自带的AdventureWorks数据库中的2个表为例
HumanResources.Department --部门信息表
HumanResources.EmployeeDepartmentHistory --部门员工对照表
--使用自定义函数的方式
SELECT groupname,dbo.fn_concatemployees(departmentid) employeesconcat FROM HumanResources.Department CREATE FUNCTION fn_concatemployees(@departmentid INT) RETURNS VARCHAR(1000) AS BEGIN DECLARE @employeeidcancat AS VARCHAR(1000); SET @employeeidcancat=''; SELECT @employeeidcancat=@employeeidcancat+CAST(employeeid AS VARCHAR(10))+';' FROM HumanResources.EmployeeDepartmentHistory WHERE departmentid=@departmentid; RETURN @employeeidcancat; END |
--使用sqlServer2005的FOR XML PATH方式
SELECT groupname, (SELECT CAST(o.employeeid AS VARCHAR(10))+';' AS [text()] FROM HumanResources.EmployeeDepartmentHistory o WHERE o.departmentid=c.departmentid ORDER BY employeeid FOR XML PATH('')) AS employeesconcat FROM HumanResources.Department c |
--在Oracle10g中采用wmsys.wm_concat方式
SELECT groupname,wmsys.wm_concat(employeeid) employeesconcat FROM EmployeeDepartmentHistory GROUP BY groupname; |
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