问题
Question: I want to write a custom aggregate function that concatenates string on group by.
So that I can do a
SELECT SUM(FIELD1) as f1, MYCONCAT(FIELD2) as f2
FROM TABLE_XY
GROUP BY FIELD1, FIELD2
All I find is SQL CRL aggregate functions, but I need SQL, without CLR.
Edit:1
The query should look like this:
SELECT SUM(FIELD1) as f1, MYCONCAT(FIELD2) as f2
FROM TABLE_XY
GROUP BY FIELD0
Edit 2:
It is true that it isn\'t possible without CLR.
However, the subselect answer by astander can be modified so it doesn\'t XML-encode special characters.
The subtle change for this is to add this after \"FOR XML PATH\": ,
TYPE
).value(\'.[1]\', \'nvarchar(MAX)\')
Here a few examples
DECLARE @tT table([A] varchar(200), [B] varchar(200));
INSERT INTO @tT VALUES (\'T_A\', \'C_A\');
INSERT INTO @tT VALUES (\'T_A\', \'C_B\');
INSERT INTO @tT VALUES (\'T_B\', \'C_A\');
INSERT INTO @tT VALUES (\'T_C\', \'C_A\');
INSERT INTO @tT VALUES (\'T_C\', \'C_B\');
INSERT INTO @tT VALUES (\'T_C\', \'C_C\');
SELECT
A AS [A]
,
(
STUFF
(
(
SELECT DISTINCT
\', \' + tempT.B AS wtf
FROM @tT AS tempT
WHERE (1=1)
--AND tempT.TT_Status = 1
AND tempT.A = myT.A
ORDER BY wtf
FOR XML PATH, TYPE
).value(\'.[1]\', \'nvarchar(MAX)\')
, 1, 2, \'\'
)
) AS [B]
FROM @tT AS myT
GROUP BY A
SELECT
(
SELECT
\',äöü<>\' + RM_NR AS [text()]
FROM T_Room
WHERE RM_Status = 1
ORDER BY RM_NR
FOR XML PATH(\'\')
) AS XmlEncodedNoNothing
,
SUBSTRING
(
(
SELECT
\',äöü<>\' + RM_NR AS [data()]
FROM T_Room
WHERE RM_Status = 1
ORDER BY RM_NR
FOR XML PATH(\'\')
)
,2
,10000
) AS XmlEncodedSubstring
,
(
STUFF
(
(
SELECT \',äöü<>\' + RM_NR + CHAR(10)
FROM T_Room
WHERE RM_Status = 1
ORDER BY RM_NR
FOR XML PATH, TYPE
).value(\'.[1]\', \'nvarchar(MAX)\')
, 1, 1, \'\'
)
) AS XmlDecodedStuffInsteadSubstring
回答1:
You cannot write custom aggregates outside of the CLR.
The only type of functions you can write in pure T-SQL are scalar and table valued functions.
Compare the pages for CREATE AGGREGATE, which only lists CLR style options, with CREATE FUNCTION, which shows T-SQL and CLR options.
回答2:
Have a look at something like. This is not an aggregate function. If you wish to implement your own aggregate function, it will have to be CLR...
DECLARE @Table TABLE(
ID INT,
Val VARCHAR(50)
)
INSERT INTO @Table (ID,Val) SELECT 1, 'A'
INSERT INTO @Table (ID,Val) SELECT 1, 'B'
INSERT INTO @Table (ID,Val) SELECT 1, 'C'
INSERT INTO @Table (ID,Val) SELECT 2, 'B'
INSERT INTO @Table (ID,Val) SELECT 2, 'C'
--Concat
SELECT t.ID,
SUM(t.ID),
stuff(
(
select ',' + t1.Val
from @Table t1
where t1.ID = t.ID
order by t1.Val
for xml path('')
),1,1,'') Concats
FROM @Table t
GROUP BY t.ID
回答3:
Starting from 2017 there is built-in concatenate aggregate function STRING_AGG :)
https://docs.microsoft.com/en-us/sql/t-sql/functions/string-agg-transact-sql?view=sql-server-2017
回答4:
Found this link around concatenation which covers methods like
Concatenating values when the number of items are not known
- Recursive CTE method
- The blackbox XML methods
- Using Common Language Runtime
- Scalar UDF with recursion
- Table valued UDF with a WHILE loop
- Dynamic SQL
- The Cursor approach
Non-reliable approaches
- Scalar UDF with t-SQL update extension
- Scalar UDF with variable concatenation in SELECT
Though it doesn't cover aggerate functions there may be some use around concatenation in there to help you with your problem.
回答5:
This solution works with no need of deploy from Visual studio or dll file in server.
Copy-Paste and it Work!
http://groupconcat.codeplex.com/
dbo.GROUP_CONCAT(VALUE )
dbo.GROUP_CONCAT_D(VALUE ), DELIMITER )
dbo.GROUP_CONCAT_DS(VALUE , DELIMITER , SORT_ORDER )
dbo.GROUP_CONCAT_S(VALUE , SORT_ORDER )
回答6:
You could do something like what I have done below to create a custom aggregate concatenation function in pure T-SQL. Obviously I have gone with a hard coded table name and group by column but it should illustrate the approach. There is probably some way to make this a truly generic function using dynamic TSQL constructed from input parameters.
/*
User defined function to help perform concatenations as an aggregate function
Based on AdventureWorks2008R2 SalesOrderDetail table
*/
--select * from sales.SalesOrderDetail
IF EXISTS (SELECT *
FROM sysobjects
WHERE name = N'fnConcatenate')
DROP FUNCTION fnConcatenate
GO
CREATE FUNCTION fnConcatenate
(
@GroupByValue int
)
returnS varchar(8000)
as
BEGIN
DECLARE @SqlString varchar(8000)
Declare @TempStore varchar(25)
select @SqlString =''
Declare @MyCursor as Cursor
SET @MyCursor = CURSOR FAST_FORWARD
FOR
Select ProductID
From sales.SalesOrderDetail where SalesOrderID = @GroupByValue
order by SalesOrderDetailID asc
OPEN @MyCursor
FETCH NEXT FROM @MyCursor
INTO @TempStore
WHILE @@FETCH_STATUS = 0
BEGIN
select @SqlString = ltrim(rtrim(@TempStore )) +',' + ltrim(rtrim(@SqlString))
FETCH NEXT FROM @MyCursor INTO @TempStore
END
CLOSE @MyCursor
DEALLOCATE @MyCursor
RETURN @SqlString
END
GO
select SalesOrderID, Sum(OrderQty), COUNT(*) as DetailCount , dbo.fnConcatenate(salesOrderID) as ConCatenatedProductList
from sales.SalesOrderDetail
where salesOrderID= 56805
group by SalesOrderID
来源：https://stackoverflow.com/questions/4374709/custom-aggregate-function-concat-in-sql-server