Flattening a Single Table - sql

Question

I am looking for a very basic flattening. I have a table in the database which provides each field for the employee in a different row.
EX
EMPLOYEE GROUP_NAME
81 BNEEO55
81 BNELLIG
81 LPKAPE
81 HRFT
90 BNRETINV
....
I would like to create a view which reports the data as:
EMPLOYEE Group1 Group2 Group3 Group4 Group5
81 BNEEO55 BNELLIG LPKAPE HRFT NULL
90 NULL NULL NULL NULL BNRETINV
OR
EMPLOYEE BNEEO55 BNELLIG LPKAPE HRFT BNRETINV
81 YES YES YES YES NO
90 NO NO NO NO YES

Answer 1

You need to PIVOT the data, if you are using SQL-Server 2008 or later you can use the PIVOT function:
CREATE TABLE #T (Employee INT, Group_name VARCHAR(50))
INSERT #T VALUES (81, 'BNEEO55'), (81, 'BNELLIG'), (81, 'LPKAPE'), (81, 'HRFT'), (90, 'BNRETINV')
SELECT Employee,
COALESCE([BNEEO55],'No') AS [BNEEO55],
COALESCE([BNELLIG],'No') AS [BNELLIG],
COALESCE([BNRETINV],'No') AS [BNRETINV],
COALESCE([HRFT],'No') AS [HRFT],
COALESCE([LPKAPE],'No') AS [LPKAPE]
FROM ( SELECT *, 'Yes' [Data]
FROM #T
) d
PIVOT
( MAX(Data)
FOR Group_Name IN ([BNEEO55], [BNELLIG], [BNRETINV], [HRFT], [LPKAPE])
) pvt
But it sounds like you need to do it dynamically if your data is changing. Something like the following would work:
DECLARE #SQL NVARCHAR(MAX) = '',
#Cols NVARCHAR(MAX) = ''
SELECT #SQL = #SQL + ',' + QUOTENAME(Group_Name),
#Cols = #Cols + ',COALESCE(' + QUOTENAME(Group_Name) + ',''No'') AS ' + QUOTENAME(Group_Name)
FROM ( SELECT DISTINCT Group_Name
FROM #T
) T
SET #SQL = '
SELECT Employee, ' + STUFF(#Cols, 1, 1, '') +
'FROM ( SELECT *, ''Yes'' [Data]
FROM #T
) d
PIVOT
( MAX(Data)
FOR Group_Name IN (' + STUFF(#SQL, 1, 1, '') + ')
) pvt'
EXECUTE SP_EXECUTESQL #SQL
This builds up the same query as the first one, but means that when a new group name is added the query doesn't have to be altered.
EDIT
To create and call this as a stored procedure:
CREATE TABLE T (Employee INT, Group_name VARCHAR(50))
INSERT T VALUES (81, 'BNEEO55'), (81, 'BNELLIG'), (81, 'LPKAPE'), (81, 'HRFT'), (90, 'BNRETINV')
GO
CREATE PROCEDURE PivotT
AS
DECLARE #SQL NVARCHAR(MAX) = '',
#Cols NVARCHAR(MAX) = ''
SELECT #SQL = #SQL + ',' + QUOTENAME(Group_Name),
#Cols = #Cols + ',COALESCE(' + QUOTENAME(Group_Name) + ',''No'') AS ' + QUOTENAME(Group_Name)
FROM ( SELECT DISTINCT Group_Name
FROM T
) T
SET #SQL = '
SELECT Employee, ' + STUFF(#Cols, 1, 1, '') +
'FROM ( SELECT *, ''Yes'' [Data]
FROM T
) d
PIVOT
( MAX(Data)
FOR Group_Name IN (' + STUFF(#SQL, 1, 1, '') + ')
) pvt'
EXECUTE SP_EXECUTESQL #SQL
GO
EXECUTE PivotT