Transposing Undefined Number of Rows to Columns - sql

Question

I have a table that looks like the following:
Member, Contract_Start, Contract_End
1, 1/1/2011, 12/30/2011
1, 1/1/2012, 12/30/2012
1, 1/1/2013, 12/30/2013
2, 7/1/2012, 12/30/2012
2, 1/1/2013, 12/30/2013
Members could have as few as 1 contract and there is no upper limit on number of contracts.
I'd like to switch the table to look like below:
Member, Contract_Start1, Contract_End1, Contract_Start2, Contract_End2.....
1, 1/1/2011, 12/30/2011, 1/1/2012, 12/30/2012
2, 7/1/2012, 12/30/2012, 1/1/2013, 12/30/2013
Thanks for any help you can give.

Answer 1

I have used such solution and would advise not to go this path because maintenance/debugging of such dynamic sql becomes to hard over long time.
you can try the demo Here
IF object_id('Test_Transpose') IS NOT NULL
DROP TABLE Test_Transpose
GO
CREATE TABLE Test_Transpose
(
memberID INT NOT NULL
,csdate datetime2(2) NULL
,cedate datetime2(2) NULL
)
INSERT INTO Test_Transpose (memberid,csdate,cedate)
SELECT 1,'1/1/2001','1/1/2001'
UNION ALL SELECT 1,'1/2/2001','1/2/2001'
UNION ALL SELECT 1,'1/3/2001','1/2/2001'
UNION ALL SELECT 1,'1/4/2001','1/2/2001'
UNION ALL SELECT 1,'1/5/2001','1/2/2001'
UNION ALL SELECT 2,'1/2/2001','1/2/2001'
UNION ALL SELECT 2,'1/3/2001','1/3/2001'
UNION ALL SELECT 3,'1/2/2001','1/2/2001'
UNION ALL SELECT 3,'1/3/2001','1/3/2001'
UNION ALL SELECT 3,'1/4/2001','1/4/2001'
UNION ALL SELECT 4,'1/2/2001','1/2/2001'
DECLARE #SQL NVARCHAR(MAX)=''
,#Startdate_SelectColumnList NVARCHAR(MAX)=''
,#EndDate_SelectColumnList NVARCHAR(MAX)=''
,#Final_SelectColumnList NVARCHAR(MAX)=''
,#PivotINColumnList NVARCHAR(MAX)=''
,#MaxContractDateCount INT=1
SELECT TOP 1 #MaxContractDateCount = COUNT(1)
FROM Test_Transpose
GROUP BY memberid
ORDER BY COUNT(1) desc
WHILE #MaxContractDateCount > 0
BEGIN
SELECT #Startdate_SelectColumnList = N'['+CAST(#MaxContractDateCount AS sysname)+N'] AS '
+N'StartDate'+CAST(#MaxContractDateCount AS sysname)
+CASE WHEN #Startdate_SelectColumnList=N'' THEN N'' ELSE N',' END
+#Startdate_SelectColumnList
SELECT #Enddate_SelectColumnList = N'['+CAST(#MaxContractDateCount AS sysname)+N'] AS '
+N'EndDate'+CAST(#MaxContractDateCount AS sysname)
+CASE WHEN #Enddate_SelectColumnList=N'' THEN N'' ELSE N',' END
+#Enddate_SelectColumnList
SELECT #Final_SelectColumnList = N'StartDate'+CAST(#MaxContractDateCount AS sysname)+N','
+N'EndDate'+CAST(#MaxContractDateCount AS sysname)
+CASE WHEN #Final_SelectColumnList=N'' THEN N'' ELSE N',' END
+#Final_SelectColumnList
SELECT #PivotINColumnList = N'['+CAST(#MaxContractDateCount AS sysname)+N']'
+CASE WHEN #PivotINColumnList=N'' THEN N'' ELSE N',' END
+#PivotINColumnList
SET #MaxContractDateCount=#MaxContractDateCount-1
END
--debug stmt
--SELECT #Startdate_SelectColumnList,#Enddate_SelectColumnList,#Final_SelectColumnList,#PivotINColumnList
SET #SQL = N'
SELECT q1.memberid,'
+#Final_SelectColumnList
+N'
FROM
(
SELECT memberid,'
+#Startdate_SelectColumnList
+N'
FROM
(
SELECT memberid,csdate,ROW_NUMBER() OVER (PARTITION BY memberid ORDER BY memberid,csdate) rowid
FROM test_transpose
)q
PIVOT
(MAX(csdate) FOR rowid IN ('+#PivotINColumnList+N'))pvt
)q1
JOIN
(
SELECT memberid,'
+#Enddate_SelectColumnList
+N'
FROM
(
SELECT memberid,cedate,ROW_NUMBER() OVER (PARTITION BY memberid ORDER BY memberid,csdate) rowid
FROM test_transpose
)q
PIVOT
(MAX(cedate) FOR rowid IN ('+#PivotINColumnList+N'))pvt
)q2
ON q1.memberid = q2.memberid
'
PRINT #SQL
EXECUTE sp_executesql #SQL

Answer 2

I have a version of Postgres db wise doing this work. Here is my sample of code.
DROP TABLE IF EXISTS x;
CREATE TABLE x ( member NUMERIC , contract_start DATE, contract_end DATE);
INSERT INTO x VALUES( 1, '1/1/2011', '12/30/2011' )
,( 1, '1/1/2012', '12/30/2012' )
,( 1, '1/1/2013', '12/30/2013' )
,( 2, '7/1/2012', '12/30/2012' )
,( 2, '1/1/2013', '12/30/2013' )
,( 3, '1/1/2012', '12/30/2012' )
,( 3, '1/1/2013', '12/30/2013' )
,( 3, '8/1/2013', '12/30/2013' )
,( 3, '8/1/2013', '12/30/2013' );
-- CREATE LANGUAGE 'plpgsql';
-- DROP SEQUENCE IF EXISTS seq;
-- CREATE SEQUENCE seq;
CREATE OR REPLACE FUNCTION make_table() RETURNS void AS
$BODY$
DECLARE
i RECORD;
colcnt INTEGER;
BEGIN
DROP TABLE IF EXISTS tmptable;
SELECT max(count) INTO colcnt FROM (SELECT count(*) FROM x GROUP BY member) a;
EXECUTE 'CREATE TABLE tmptable (member integer ,' ||
(SELECT array_to_string(array_agg(x1.col1 || ' date, ' || x1.col2 || ' date'), ', ')
FROM (SELECT 'contract_start' || col col1
, 'contract_end'|| col col2 FROM generate_series(1,colcnt) t(col) ) x1 ) || ')';
EXECUTE 'INSERT INTO tmptable (member) SELECT DISTINCT member FROM x';
FOR i IN SELECT * FROM x ORDER BY member LOOP
PERFORM setval('seq',1);
EXECUTE 'UPDATE tmptable SET ' || x1.col
FROM (SELECT array_to_string(array_agg(' contract_start'
|| nextval('seq')-1 || ' = ''' || i.contract_start || ''', contract_end'
|| currval('seq')-1 || ' = ''' || i.contract_end ), ''', ') || ''' WHERE member = ' || member || ';' col
FROM x WHERE member = i.member GROUP BY member) x1;
END LOOP;
END;
$BODY$ LANGUAGE plpgsql;
SELECT * FROM make_table();
SELECT * FROM tmptable;
This is the first time I am answering. Hope this is relevant. (please run the commented only once).
Further the process of calling function each time on insert, update or delete can be automated with trigger. The following code will do that on replace of above one.
-- following commented lines for first time run :
-- CREATE LANGUAGE 'plpgsql';
-- DROP SEQUENCE IF EXISTS seq;
-- CREATE SEQUENCE seq;
-- DROP FUNCTION IF EXISTS make_table();
CREATE OR REPLACE FUNCTION make_table() RETURNS TRIGGER AS
$BODY$
DECLARE
i RECORD;
colcnt INTEGER;
BEGIN
DROP TABLE IF EXISTS tmptable;
SELECT max(count) INTO colcnt FROM (SELECT count(*) FROM x GROUP BY member) a;
EXECUTE 'CREATE TABLE tmptable (member integer ,' ||
(SELECT array_to_string(array_agg(x1.col1 || ' date, ' || x1.col2 || ' date'), ', ')
FROM (SELECT 'contract_start' || col col1
, 'contract_end'|| col col2 FROM generate_series(1,colcnt) t(col) ) x1 ) || ')';
EXECUTE 'INSERT INTO tmptable (member) SELECT DISTINCT member FROM x';
FOR i IN SELECT * FROM x ORDER BY member LOOP
PERFORM setval('seq',1);
EXECUTE 'UPDATE tmptable SET ' || x1.col
FROM (SELECT array_to_string(array_agg(' contract_start'
|| nextval('seq')-1 || ' = ''' || i.contract_start || ''', contract_end'
|| currval('seq')-1 || ' = ''' || i.contract_end ), ''', ') || ''' WHERE member = ' || member || ';' col
FROM x WHERE member = i.member GROUP BY member) x1;
END LOOP;
RETURN new;
END;
$BODY$ LANGUAGE plpgsql;
CREATE TRIGGER create_tmptable AFTER INSERT OR UPDATE OR DELETE OR TRUNCATE
ON x FOR STATEMENT EXECUTE PROCEDURE make_table();
-- For Test insert:
INSERT INTO x VALUES( 4, '1/1/2011', '12/30/2011' );
SELECT * FROM tmptable;