SQL Server 等效于 GROUP_CONCAT() [重复]答案

【问题标题】：SQL Server equivalent to GROUP_CONCAT() [duplicate]SQL Server 等效于 GROUP_CONCAT() [重复]
【发布时间】：2013-10-07 07:09:03
【问题描述】：

我有这个数据库：

我需要为每个客户获取以下数据：

客户名称
合同名称
项目
从当月第一天到当月最后一天记录项目小时数的员工
每个员工在当月记录的总小时数
员工率
每位员工的总费用（即员工费率 x 员工工作时间）
每份合同的帐单联系人 [姓名、地址]

到目前为止，我有以下查询，但我需要实现 MySQL 的 GROUP_CONCAT( ) 的 MSSQL 版本

SELECT 

Cl.LegalName AS ClientNames,
Cr.ContractDesc AS ContractNames,
P.ProjectName AS ProjectNames,
( E.FirstName + ' ' + E.LastName ) AS EmployeeNames,
SUM( WH.HoursWorked ) AS TotalHours, 
( SUM( WH.HoursWorked ) * BR.Rate ) AS TotalCharges, 
( Ca.FirstName + Ca.LastName + ', ' + Ca.AddrLine1 ) AS BillingContacts

FROM Clients Cl
JOIN Contracts Cr
ON( Cl.ClientID = Cr.ClientID )

JOIN Projects P 
ON( Cr.ContractID = P.ContractID )

JOIN EmployeesProjects EP
ON( P.ProjectID = EP.ProjectID )

JOIN Employees E 
ON( EP.EmpID = E.EmpID )

JOIN WorkHours WH
ON( E.EmpID = WH.EmpID )

JOIN BillingRates BR
ON( E.TitleID = BR.TitleID ) AND ( E.Level = BR.Level )

JOIN ContractsContacts CC
ON( Cr.ContractID = CC.ContractID )
JOIN Contacts Ca
ON( CC.ContactID = Ca.ContactID )

WHERE WH_Month = 4
AND WH_Year = 2013

当我开始关注 this 示例时，我到了这里并停下来，因为我意识到我无法从其他子查询 (ProjectNames) 引用表别名 (Cr)。

SELECT 
Cl.LegalName AS ClientNames, 
(
    SELECT ContractDesc + ', '
    FROM Contracts Cr
    WHERE Cl.ClientID = Cr.ClientID 
    FOR XML PATH('')
) ContractNames,
(
    SELECT ProjectName + ', '
    FROM Projects P
    WHERE Cr.ContractID = P.ContractID
    FOR XML PATH('')
) ProjectNames


FROM Clients Cl

我该如何做呢？

【问题讨论】：

标签： sql sql-server join string-aggregation

【解决方案1】：

尝试CROSS APPLY做你自己：

例如：

SELECT Cl.LegalName AS ClientNames,
B.ContractDesc AS ContractNames,
P.ProjectName AS ProjectNames,
( E.FirstName + ' ' + E.LastName ) AS EmployeeNames,
SUM( WH.HoursWorked ) AS TotalHours, 
( SUM( WH.HoursWorked ) * BR.Rate ) AS TotalCharges, 
( Ca.FirstName + Ca.LastName + ', ' + Ca.AddrLine1 ) AS BillingContacts

FROM Clients Cl
JOIN Contracts Cr ON( Cl.ClientID = Cr.ClientID )
JOIN Projects P ON( Cr.ContractID = P.ContractID )
JOIN EmployeesProjects EP ON( P.ProjectID = EP.ProjectID )
JOIN Employees E ON( EP.EmpID = E.EmpID )
JOIN WorkHours WH ON( E.EmpID = WH.EmpID )
JOIN BillingRates BR ON( E.TitleID = BR.TitleID ) AND ( E.Level = BR.Level )
JOIN ContractsContacts CC ON( Cr.ContractID = CC.ContractID )
JOIN Contacts Ca ON( CC.ContactID = Ca.ContactID ) 
CROSS APPLY (
    SELECT Cr1.ContractDesc + ', '
    FROM Contracts Cr1
    WHERE Cl.ClientID = Cr1.ClientID 
    FOR XML PATH('')
) B (ContractDesc)
WHERE WH_Month = 4 AND WH_Year = 2013

【讨论】：

【解决方案2】：

这样做

   SELECT Cl.LegalName AS ClientNames,
   ContractNames
   FROM Clients Cl
    cross apply 
   (SELECT Cr1.ContractDesc + ', '
    FROM Contracts Cr1
      WHERE Cl.ClientID = Cr1.ClientID  For XML PATH(''))a1 (ContractNames)

【讨论】：

【解决方案3】：

STRING_AGG 几乎等同于 MySQL 中的 GROUP_CONCAT。参考微软官方文档here

请注意，STRING_AGG 不允许 Text 类型，因此如果要在 Text 字段上连接，则需要转换为 NVARCHAR。

例子：

STRING_AGG(CONVERT(NVARCHAR(2000), your_text_field_name), ',')

【讨论】：