背景：在做項目時，經常會遇到這樣的表結構在主表的中有一列保存的是用逗號隔開ID。如，當一個員工從屬多個部門時、當一個項目從屬多個城市時、當一個設備從屬多個項目時，很多人都會在員工表中加入一個deptIds VARCHAR(1000)列（本文以員工從屬多個部門為例），用以保存部門編號列表（很明顯這不符合第一范式，但很多人這樣設計了，在這篇文章中我們暫不討論在這種應用場景下，如此設計的對與錯，有興趣的可以在回復中聊聊），然後我們在查詢列表中需要看到這個員工從屬哪些部門。
初始化數據：
部門表、員工表數據：
復制代碼 代碼如下:
IF EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[Department]'))
DROP TABLE [dbo].Department
GO
--部門表
CREATE TABLE Department
(
id int,
name nvarchar(50)
)
INSERT INTO Department(id,name)
SELECT 1,'人事部'
UNION
SELECT 2,'工程部'
UNION
SELECT 3,'管理部'
SELECT * FROM Department
IF EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[Employee]'))
DROP TABLE [dbo].Employee
GO
--員工表
CREATE TABLE Employee
(
id int,
name nvarchar(20),
deptIds varchar(1000)
)
INSERT INTO Employee(id,name,deptIds)
SELECT 1,'蔣大華','1,2,3'
UNION
SELECT 2,'小明','1'
UNION
SELECT 3,'小華',''
SELECT * FROM Employee
希望得到的結果：
解決方法：
第一步，是得到如下的數據。即將員工表集合與相關的部門集合做交叉連接，其中使用了fun_SplitIds函數（作用是將ids分割成id列表），然後員工集合與這個得到的集合做交叉連接
復制代碼 代碼如下:
SELECT E.*,ISNULL(D.name,'') AS deptName
FROM Employee AS E
OUTER APPLY dbo.fun_SplitIds(E.deptIds) AS DID
LEFT JOIN Department AS D ON DID.ID=D.id;
第二步，已經得到了如上的數據，然後要做的就是根據ID分組，並對deptName列做聚合操作，但可惜的是SQL SERVER還沒有提供對字符串做聚合的操作。但想到，我們處理樹形結構數據時，用CTE來做關系數據，做成有樹形格式的數據，如此我們也可以將這個問題轉換成做樹形格式的問題，代碼如下：
復制代碼 代碼如下:
;WITH EmployeT AS(
--員工的基本信息(使用OUTER APPLY將多個ID拆分開來,然後與部門表相關聯)
--此時已將員工表所存的IDS分別與部門相關聯,下面需要將此集合中的deptName聚合成一個記錄
SELECT E.*,ISNULL(D.name,'') AS deptName
FROM Employee AS E
OUTER APPLY dbo.fun_SplitIds(E.deptIds) AS DID
LEFT JOIN Department AS D ON DID.ID=D.id
),mike AS(
SELECT id,name,deptIds,deptName
,ROW_NUMBER()OVER(PARTITION BY id ORDER BY id) AS level_num
FROM EmployeT
),mike2 AS(
SELECT id,name,deptIds,CAST(deptName AS NVARCHAR(100)) AS deptName,level_num
FROM mike
WHERE level_num=1
UNION ALL
SELECT m.id,m.name,m.deptIds,CAST(m2.deptName+','+m.deptName AS NVARCHAR(100)) AS deptName,m.level_num
FROM mike AS m
INNER JOIN mike2 AS m2 ON m.ID=m2.id AND m.level_num=m2.level_num+1
),maxMikeByIDT AS(
SELECT id,MAX(level_num) AS level_num
FROM mike2
GROUP BY ID
)
SELECT A.id,A.name,A.deptIds,A.deptName
FROM mike2 AS A
INNER JOIN maxMikeByIDT AS B ON A.id=B.ID AND A.level_num=B.level_num
ORDER BY A.id OPTION (MAXRECURSION 0)
結果如下：
全部SQL：
復制代碼 代碼如下:
IF EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[Department]'))
DROP TABLE [dbo].Department
GO
--部門表
CREATE TABLE Department
(
id int,
name nvarchar(50)
)
INSERT INTO Department(id,name)
SELECT 1,'人事部'
UNION
SELECT 2,'工程部'
UNION
SELECT 3,'管理部'
SELECT * FROM Department
IF EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[Employee]'))
DROP TABLE [dbo].Employee
GO
--員工表
CREATE TABLE Employee
(
id int,
name nvarchar(20),
deptIds varchar(1000)
)
INSERT INTO Employee(id,name,deptIds)
SELECT 1,'蔣大華','1,2,3'
UNION
SELECT 2,'小明','1'
UNION
SELECT 3,'小華',''
SELECT * FROM Employee
--創建一個表值函數，用來拆分用逗號分割的數字串，返回只有一列數字的表
IF EXISTS (SELECT * FROM sys.objects WHERE object_id = OBJECT_ID(N'[dbo].[fun_SplitIds]'))
DROP FUNCTION [dbo].fun_SplitIds
GO
CREATE FUNCTION dbo.fun_SplitIds(
@Ids nvarchar(1000)
)
RETURNS @t_id TABLE (id VARCHAR(36))
AS
BEGIN
DECLARE @i INT,@j INT,@l INT,@v VARCHAR(36);
SET @i = 0;
SET @j = 0;
SET @l = len(@Ids);
while(@j < @l)
begin
SET @j = charindex(',',@Ids,@i+1);
IF(@j = 0) set @j = @l+1;
SET @v = cast(SUBSTRING(@Ids,@i+1,@j-@i-1) as VARCHAR(36));
INSERT INTO @t_id VALUES(@v)
SET @i = @j;
END
RETURN;
END
GO
;WITH EmployeT AS(
--員工的基本信息(使用OUTER APPLY將多個ID拆分開來,然後與部門表相關聯)
--此時已將員工表所存的IDS分別與部門相關聯,下面需要將此集合中的deptName聚合成一個記錄
SELECT E.*,ISNULL(D.name,'') AS deptName
FROM Employee AS E
OUTER APPLY dbo.fun_SplitIds(E.deptIds) AS DID
LEFT JOIN Department AS D ON DID.ID=D.id
),mike AS(
SELECT id,name,deptIds,deptName
,ROW_NUMBER()OVER(PARTITION BY id ORDER BY id) AS level_num
FROM EmployeT
),mike2 AS(
SELECT id,name,deptIds,CAST(deptName AS NVARCHAR(100)) AS deptName,level_num
FROM mike
WHERE level_num=1
UNION ALL
SELECT m.id,m.name,m.deptIds,CAST(m2.deptName+','+m.deptName AS NVARCHAR(100)) AS deptName,m.level_num
FROM mike AS m
INNER JOIN mike2 AS m2 ON m.ID=m2.id AND m.level_num=m2.level_num+1
),maxMikeByIDT AS(
SELECT id,MAX(level_num) AS level_num
FROM mike2
GROUP BY ID
)
SELECT A.id,A.name,A.deptIds,A.deptName
FROM mike2 AS A
INNER JOIN maxMikeByIDT AS B ON A.id=B.ID AND A.level_num=B.level_num
ORDER BY A.id OPTION (MAXRECURSION 0)
