How do I accumulate values in T-SQL? AFAIK there is no ARRAY type.
I want to re-use the values in the same query like demonstrated in this PostgreSQL example using array_agg().
SELECT a[1] || a[i] AS foo
, a[2] || a[5] AS bar -- assuming we have >= 5 rows for simplicity
FROM (
SELECT array_agg(text_col ORDER BY text_col) AS a
, count(*)::int4 AS i
FROM tbl
WHERE id BETWEEN 10 AND 100
) sub;
How would I best solve this with T-SQL?
Best I could come up with are two CTE and subselects:
;WITH x AS (
SELECT row_number() OVER (ORDER BY name) AS rn
, name AS a
FROM #t
WHERE id BETWEEN 10 AND 100
)
, i AS (
SELECT count(*) AS i
FROM x
)
SELECT (SELECT a FROM x WHERE rn = 1) + (SELECT a FROM x WHERE rn = i) AS foo
, (SELECT a FROM x WHERE rn = 2) + (SELECT a FROM x WHERE rn = 5) AS bar
FROM i;
Test setup:
CREATE TABLE #t(
id INT PRIMARY KEY
, name NVARCHAR(100))
;
INSERT INTO #t VALUES
( 3, 'John')
, ( 5, 'Mary')
, ( 8, 'Michael')
, (13, 'Steve')
, (21, 'Jack')
, (34, 'Pete')
, (57, 'Ami')
, (88, 'Bob')
;
Is there a simpler way?
Edit 1: I have added another solution that shows how to simulate ARRAY_AGG on SQL Server (the last answer).
Edit 2: For the solution number 4) I have added the third method for concatenation.
I'm not sure I have I understood correctly your question.
a) Instead of using arrays in SQL Server I would use table variables or XML.
b) To concatenate strings (in this case) I would use SELECT @var = @var + Name FROM tbl statements or XML xqueries.
c) The solution based on CTEs and multiple subqueries (WITH cte AS () FROM SELECT (SELECT * FROM cte.rn=1) + ()...) will generates a lot of scans and logical reads.
Solutions:
1) Table variable + SELECT @var = @var + Name FROM tbl:
--Creating the "array"
DECLARE @Array TABLE
(
Idx INT PRIMARY KEY,
Val NVARCHAR(100) NOT NULL
);
WITH Base
AS
(
SELECT Val = t.name,
Idx = ROW_NUMBER() OVER(ORDER BY t.name ASC)
FROM #t t
WHERE t.id between 10 AND 100
)
INSERT @Array (Idx, Val)
SELECT b.Idx, b.Val
FROM Base b;
--Concatenating all names
DECLARE @AllNames NVARCHAR(4000);
--”Reset”/Init @AllNames
SET @AllNames = '';
--String concatenation
SELECT @AllNames = @AllNames + ',' + a.Val
FROM @Array a;
--Remove first char (',')
SELECT @AllNames = STUFF(@AllNames, 1, 1, '');
--The final result
SELECT @AllNames [Concatenating all names - using a table variable];
/*
Concatenating all names - using a table variable
------------------------------------------------
Ami,Bob,Jack,Pete,Steve
*/
--Concatenating Idx=2 and Idx=5
--”Reset” @AllNames value
SET @AllNames = '';
--String concatenation
SELECT @AllNames = @AllNames + ',' + a.Val
FROM @Array a
WHERE a.Idx IN (2,5) --or a.Idx IN (2, (SELECT COUNT(*) FROM @Array))
ORDER BY a.Idx ASC;
--Remove first char (',')
SELECT @AllNames = STUFF(@AllNames, 1, 1, '');
--The final result
SELECT @AllNames [Concatenating Idx=2 and Idx=5 - using a table variable];
/*
Concatenating Idx=2 and Idx=5 - using a table variable
------------------------------------------------------
Bob,Steve
*/
2) Table variable + PIVOT:
--Concatenating a finite number of elements (names)
SELECT pvt.[1] + ',' + pvt.[0] AS [PIVOT Concat_1_and_i(0)]
,pvt.[2] + ',' + pvt.[5] AS [PIVOT Concat_2_and_5]
,pvt.*
FROM
(
SELECT a.Idx, a.Val
FROM @Array a
WHERE a.Idx IN (1,2,5)
UNION ALL
SELECT 0, a.Val --The last element has Idx=0
FROM @Array a
WHERE a.Idx = (SELECT COUNT(*) FROM @Array)
) src
PIVOT (MAX(src.Val) FOR src.Idx IN ([1], [2], [5], [0])) pvt;
/*
PIVOT Concat_1_and_i(0) PIVOT Concat_2_and_5
----------------------- --------------------
Ami,Steve Bob,Steve
*/
3) XML + XQuery:
SET ANSI_WARNINGS ON;
GO
DECLARE @x XML;
;WITH Base
AS
(
SELECT Val = t.name,
Idx = ROW_NUMBER() OVER(ORDER BY t.name ASC)
FROM #t t
WHERE t.id BETWEEN 10 AND 100
)
SELECT @x =
(
SELECT b.Idx AS [@Idx]
,b.Val AS [text()]
FROM Base b
FOR XML PATH('Element'), ROOT('Array')
);
/* @x content
<Array>
<Element Idx="1">Ami</Element>
<Element Idx="2">Bob</Element>
<Element Idx="3">Jack</Element>
<Element Idx="4">Pete</Element>
<Element Idx="5">Steve</Element>
</Array>
*/
--Concatenating all names (the result is XML, so a cast is needed)
DECLARE @r XML; --XML result
SELECT @r=@x.query('
(: $e = array element :)
for $e in (//Array/Element)
return string($e)
');
SELECT REPLACE(CONVERT(NVARCHAR(4000), @r), ' ', ',') AS [Concatenating all names - using XML];
/*
Concatenating all names - using XML
-----------------------------------
Ami,Bob,Jack,Pete,Steve
*/
--Concatenating Idx=1 and all names
SELECT @r=@x.query('
(: $e = array element :)
for $e in (//Array/Element[@Idx=1], //Array/Element)
return string($e)
');
SELECT REPLACE(CONVERT(NVARCHAR(4000), @r), ' ', ',') AS [Concatenating Idx=1 and all names - using XML];
/*
Concatenating Idx=1 and all names - using XML
---------------------------------------------
Ami,Ami,Bob,Jack,Pete,Steve
*/
--Concatenating Idx=1 and i(last name)
DECLARE @i INT;
SELECT @r=@x.query('
(: $e = array element :)
for $e in (//Array/Element[@Idx=1], //Array/Element[@Idx=count(//Array/Element)])
return string($e)
');
SELECT REPLACE(CONVERT(NVARCHAR(4000), @r), ' ', ',') AS [Concatenating Idx=1 and i(last name) - using XML];
/*
Concatenating Idx=1 and i(last name) - using XML
------------------------------------------------
Ami,Steve
*/
--Concatenating Idx=2 and Idx=5
SELECT @r=@x.query('
(: $e = array element :)
for $e in (//Array/Element[@Idx=2], //Array/Element[@Idx=5])
return string($e)
');
SELECT REPLACE(CONVERT(NVARCHAR(4000), @r), ' ', ',') AS [Concatenating Idx=2 and Idx=5 - using XML (method 1)];
/*
Concatenating Idx=2 and Idx=5 - using XML (method 1)
----------------------------------------------------
Bob,Steve
*/
--Concatenating Idx=2 and Idx=5
SELECT @x.value('(//Array/Element)[@Idx=2][1]', 'NVARCHAR(100)')
+ ','
+ @x.value('(//Array/Element)[@Idx=5][1]', 'NVARCHAR(100)') AS [Concatenating Idx=2 and Idx=5 - using XML (method 2)];;
/*
Concatenating Idx=2 and Idx=5 - using XML (method 2)
----------------------------------------------------
Bob,Steve
*/
4) If the question is how to simulate ARRAY_AGG on SQL Server then, one answer might be: by using XML.
Example:
SET ANSI_WARNINGS ON;
GO
DECLARE @Test TABLE
(
Id INT PRIMARY KEY
,GroupID INT NOT NULL
,Name NVARCHAR(100) NOT NULL
);
INSERT INTO @Test (Id, GroupID, Name)
VALUES
(3 , 1, 'John')
,(5 , 1, 'Mary')
,(8 , 1, 'Michael')
,(13, 1, 'Steve')
,(21, 1, 'Jack')
,(34, 2, 'Pete')
,(57, 2, 'Ami')
,(88, 2, 'Bob');
WITH BaseQuery
AS
(
SELECT a.GroupID, a.Name
FROM @Test a
WHERE a.Id BETWEEN 10 AND 100
)
SELECT x.*
, CONVERT(XML,x.SQLServer_Array_Agg).query
('
for $e in (//Array/Element[@Idx=1], //Array/Element[@Idx=count(//Array/Element)])
return string($e)
') AS [Concat Idx=1 and Idx=i (method 1)]
, CONVERT(XML,x.SQLServer_Array_Agg).query('
let $a := string((//Array/Element[@Idx=1])[1])
let $b := string((//Array/Element[@Idx=count(//Array/Element)])[1])
let $c := concat($a , "," , $b) (: " is used as a string delimiter :)
return $c
') AS [Concat Idx=1 and Idx=i (method 2)]
, CONVERT(XML,x.SQLServer_Array_Agg).query
('
for $e in (//Array/Element[@Idx=(1,count(//Array/Element))])
return string($e)
') AS [Concat Idx=1 and Idx=i (method 3)]
FROM
(
SELECT a.GroupID
,(SELECT ROW_NUMBER() OVER(ORDER BY b.Name) AS [@Idx]
,b.Name AS [text()]
FROM BaseQuery b
WHERE a.GroupID = b.GroupID
ORDER BY b.Name
FOR XML PATH('Element'), ROOT('Array') ) AS SQLServer_Array_Agg
FROM BaseQuery a
GROUP BY a.GroupID
) x;
Results:
GroupID SQLServer_Array_Agg Concat Idx=1 and Idx=i (method 1) Concat Idx=1 and Idx=i (method 2) Concat Idx=1 and Idx=i (method 3)
------- ---------------------------------------------------------------------------------------------------------- --------------------------------- --------------------------------- ---------------------------------
1 <Array><Element Idx="1">Jack</Element><Element Idx="2">Steve</Element></Array> Jack Steve Jack,Steve Jack Steve
2 <Array><Element Idx="1">Ami</Element><Element Idx="2">Bob</Element><Element Idx="3">Pete</Element></Array> Ami Pete Ami,Pete Ami Pete