SQL query with pivot tables? - sql

Question

I'm trying to wrap by brain around how to use pivot tables for a query I need. I have 3 database tables. Showing relevant columns:
TableA: Columns = pName
TableB: Columns = GroupName, GroupID
TableC: Columns = pName, GroupID
TableA contains a list of names (John, Joe, Jack, Jane)
TableB contains a list of groups with an ID#. (Soccer|1, Hockey|2, Basketball|3)
TableC contains a list of the names and the group they belong to (John|1, John|3, Joe|2, Jack|1, Jack|2, Jack|3, Jane|3)
I need to create a matrix like grid view using a SQL query that would return a list of all the names from TableA (Y-axis) and a list of all the possible groups (X-axis). The cell values would be either true or false if they belong to the group.
Any help would be appreciated. I couldn't quite find an existing answer that helped.

Answer 1

You might try it like this
Here I set up a MCVE, please try to create this in your next question yourself...
DECLARE #Name TABLE (pName VARCHAR(100));
INSERT INTO #Name VALUES('John'),('Joe'),('Jack'),('Jane');
DECLARE #Group TABLE(gName VARCHAR(100),gID INT);
INSERT INTO #Group VALUES ('Soccer',1),('Hockey',2),('Basketball',3);
DECLARE #map TABLE(pName VARCHAR(100),gID INT);
INSERT INTO #map VALUES
('John',1),('John',3)
,('Joe',2)
,('Jack',1),('Jack',2),('Jack',3)
,('Jane',3);
This quer will collect the values and perform PIVOT
SELECT p.*
FROM
(
SELECT n.pName
,g.gName
,'x' AS IsInGroup
FROM #map AS m
INNER JOIN #Name AS n ON m.pName=n.pName
INNER JOIN #Group AS g ON m.gID=g.gID
) AS x
PIVOT
(
MAX(IsInGroup) FOR gName IN(Soccer,Hockey,Basketball)
) as p
This is the result.
pName Soccer Hockey Basketball
Jack x x x
Jane NULL NULL x
Joe NULL x NULL
John x NULL x
Some hints:
You might use 1 and 0 instead of x as SQL Server does not know a real boolean
You should add a pID to your names. Never join tables on real data (unless it is something unique and unchangeable [which means never acutally!!!])
UPDATE dynamic SQL (thx to #djlauk)
If you want a query which deals with any amount of groups you have to to this dynamically. But please be aware, that you loose the chance to use this in ad-hoc-SQL like in VIEW or inline TVF, which is quite a big backdraw...
CREATE TABLE #Name(pName VARCHAR(100));
INSERT INTO #Name VALUES('John'),('Joe'),('Jack'),('Jane');
CREATE TABLE #Group(gName VARCHAR(100),gID INT);
INSERT INTO #Group VALUES ('Soccer',1),('Hockey',2),('Basketball',3);
CREATE TABLE #map(pName VARCHAR(100),gID INT);
INSERT INTO #map VALUES
('John',1),('John',3)
,('Joe',2)
,('Jack',1),('Jack',2),('Jack',3)
,('Jane',3);
DECLARE #ListOfGroups VARCHAR(MAX)=
(
STUFF
(
(
SELECT DISTINCT ',' + QUOTENAME(gName)
FROM #Group
FOR XML PATH('')
),1,1,''
)
);
DECLARE #sql VARCHAR(MAX)=
(
'SELECT p.*
FROM
(
SELECT n.pName
,g.gName
,''x'' AS IsInGroup
FROM #map AS m
INNER JOIN #Name AS n ON m.pName=n.pName
INNER JOIN #Group AS g ON m.gID=g.gID
) AS x
PIVOT
(
MAX(IsInGroup) FOR gName IN(' + #ListOfGroups + ')
) as p');
EXEC(#sql);
GO
DROP TABLE #map;
DROP TABLE #Group;
DROP TABLE #Name;

Answer 2

I suspect it may be laborious to keep the pivot up to date if categories are added. Or maybe I just prefer Excel (if you ignore one major advantage). The following approach could be helpful too, assuming you do have Office 365.
I added the three tables using 3 CREATE TABLE statements and 3 INSERT statements based on the code I saw above. (The solutions make use of temporary tables to insert specific values, but I believe you already have the data in your three tables, called TableA, TableB, TableC).
CREATE TABLE TestName (pName VARCHAR(100));
INSERT INTO TestName VALUES('John'),('Joe'),('Jack'),('Jane');
CREATE TABLE TestGroup (gName VARCHAR(100),gID INT);
INSERT INTO TestGroup VALUES ('Soccer',1),('Hockey',2),('Basketball',3);
CREATE TABLE Testmap (pName VARCHAR(100),gID INT);
INSERT INTO Testmap VALUES
('John',1),('John',3)
,('Joe',2)
,('Jack',1),('Jack',2),('Jack',3)
,('Jane',3);
Then, in MS Excel, I added (there may be a shorter sequence but I'm still exploring) the three tables as queries from database > sql server database. After adding them, I added all three to the Data Model (I can elaborate if you ask).
I then inserted PivotTable from the ribbon, chose External data source, but opened the Tables tab (instead of Connections tab), to find my data model (mine was top of the list) and I clicked Open. At some point Excel prompted me to create relationships between tables and it did a good job of auto generating them for me.
After minor tweaks my PivotTable came out like this (I could also ask Excel to show the data as a PivotChart).
Pivot showing groups as columns and names as rows.
The advantage is that you don't have to revisit the PIVOT code in SQL if the list (of groups) changes. As I think someone else mentioned, consider using ids for pName as well, or another way to ensure that you are not stuck the next day if you have two persons named John or Jack.
In Excel you can choose when to refresh the data (or the pivot) and, after refresh, any additional categories will be added and counted.