Concatenating rows in a multi-column format in T-SQL [duplicate] - sql-server

Question

This question already has answers here:
Simulating group_concat MySQL function in Microsoft SQL Server 2005?
(12 answers)
Closed 6 years ago.
If there is a table called employee
EmpID EmpName
---------- -------------
1 Mary
1 John
1 Sam
2 Alaina
2 Edward
Result I need in this format:
EmpID EmpName
---------- -------------
1 Mary, John, Sam
2 Alaina, Edward
Q: this record is in same Employee table. I have almost no experience using UDFs, stored procedures, I need to be done this thing through query.Is this possible without using UDFs, SP's.

Answer 1

FOR XML PATH trick and article
CLR User defined aggregate
for sql server prior version 2005 - temporary tables
An example of #1
DECLARE #t TABLE (EmpId INT, EmpName VARCHAR(100))
INSERT #t VALUES
(1, 'Mary'),(1, 'John'),(1, 'Sam'),(2, 'Alaina'),(2, 'Edward')
SELECT distinct
EmpId,
(
SELECT EmpName+','
FROM #t t2
WHERE t2.EmpId = t1.EmpId
FOR XML PATH('')
) Concatenated
FROM #t t1
How to strip the final comma - is on your own
A CLR aggregate c# code for #2
using System;
using System.Collections.Generic;
using System.Data.SqlTypes;
using System.Text;
using Microsoft.SqlServer.Server;
using System.IO;
namespace DatabaseAssembly
{
[Serializable]
[SqlUserDefinedAggregate(Format.UserDefined,
IsInvariantToNulls = true,
IsInvariantToDuplicates = true,
IsInvariantToOrder = true,
MaxByteSize = -1)]
public struct StringJoin : IBinarySerialize
{
private Dictionary<string, string> AggregationList
{
get
{
if (_list == null)
_list = new Dictionary<string, string>();
return _list;
}
}
private Dictionary<string, string> _list;
public void Init()
{
}
public void Accumulate(SqlString Value)
{
if (!Value.IsNull)
AggregationList[Value.Value.ToLowerInvariant()] = Value.Value;
}
public void Merge(StringJoin Group)
{
foreach (var key in Group.AggregationList.Keys)
AggregationList[key] = Group.AggregationList[key];
}
public SqlChars Terminate()
{
var sb = new StringBuilder();
foreach (var value in AggregationList.Values)
sb.Append(value);
return new SqlChars(sb.ToString());
}
#region IBinarySerialize Members
public void Read(System.IO.BinaryReader r)
{
try
{
while (true)
AggregationList[r.ReadString()] = r.ReadString();
}
catch (EndOfStreamException)
{
}
}
public void Write(System.IO.BinaryWriter w)
{
foreach (var key in AggregationList.Keys)
{
w.Write(key);
w.Write(AggregationList[key]);
}
}
#endregion
}
}

Answer 2

The chosen answer from #OlegDok's may return the correct result. But the performance can be terrible. This test scenario will illustrate it.
Creation of a temp table:
CREATE table #temp (EmpId INT, EmpName VARCHAR(100))
;WITH N(N)AS
(SELECT 1 FROM(VALUES(1),(1),(1),(1),(1),(1),(1),(1),(1),(1))M(N)),
tally(N)AS(SELECT ROW_NUMBER()OVER(ORDER BY N.N)FROM N,N a,N b,N c,N d,N e,N f)
INSERT #temp
SELECT EmpId, EmpName FROM (values(1, 'Mary'),(1, 'John'),(1, 'Sam')) x(EmpId, EmpName)
CROSS APPLY
(SELECT top 2000 N FROM tally) y
UNION ALL
SELECT EmpId, EmpName FROM (values(2, 'Alaina'),(2, 'Edward')) x(EmpId, EmpName)
CROSS APPLY
(SELECT top 2000 N FROM tally) y
This is only 10.000 rows. But lots of identical EmpId.
This query in Oleg's answer took 64 seconds on my database.
SELECT distinct
EmpId,
(
SELECT EmpName+','
FROM #temp t2
WHERE t2.EmpId = t1.EmpId
FOR XML PATH('')
) Concatenated
FROM #temp t1
Distinct is not the correct way of cleaning up rows in this situation.
To avoid this cartesian join, reduce the initial number of IDs before joining like this.
This is the correct way of handling this:
;WITH CTE as
(
SELECT distinct EmpId
FROM #temp
)
SELECT
EmpId,
STUFF((
SELECT ','+EmpName
FROM #temp t2
WHERE t2.EmpId = t1.EmpId
FOR XML PATH('')
), 1,1,'') Concatenated
FROM CTE t1
This takes less than 1 second

Answer 3

I think there is no GROUP_CONCAT function in MSSQL. This article shows different ways of concactenating row values.
Concatenating values when the number of items is small and known upfront
SELECT CategoryId,
MAX( CASE seq WHEN 1 THEN ProductName ELSE '' END ) + ', ' +
MAX( CASE seq WHEN 2 THEN ProductName ELSE '' END ) + ', ' +
MAX( CASE seq WHEN 3 THEN ProductName ELSE '' END ) + ', ' +
MAX( CASE seq WHEN 4 THEN ProductName ELSE '' END )
FROM ( SELECT p1.CategoryId, p1.ProductName,
( SELECT COUNT(*)
FROM Northwind.dbo.Products p2
WHERE p2.CategoryId = p1.CategoryId
AND p2.ProductName <= p1.ProductName )
FROM Northwind.dbo.Products p1 ) D ( CategoryId, ProductName, seq )
GROUP BY CategoryId ;
More ways on this link.

Answer 4

This is the solution for the example given in the beginning:
SELECT DISTINCT emp_name,
STUFF(
(SELECT ', ' + RTRIM(proj_id)
FROM project_members AS t1
WHERE t1.emp_name = t2.emp_name
FOR XML PATH (''))
, 1, 1, '')
FROM project_members t2