How can I swap rows to columns in a SELECT statement

SQL Apprentice Question
I've got dynamically changing columns in a table. One way is to define many
parameter columns in this table with the datatype nvarchar and a second
table that is defining the datatype, max and min values of these parameter
fields.

Because I want to have more flexibility I think to save the dynamically
changing columns as rows in another table.
Is there a way to retrieve the columns I saved as rows in another table as
columns?




Celko Answers
Columns do not change; SQL has strong typing. Your real problem is
that you do not have a data model or RDBMS design yet. I found an old
"cut & paste". Someone like you posted this:

CREATE TABLE EAV -- no key declared
(key_col VARCHAR (10) NULL,
attrib_value VARCHAR (50) NULL);


INSERT INTO EAV VALUES ('LOCATION','Bedroom');
INSERT INTO EAV VALUES ('LOCATION','Dining Room');
INSERT INTO EAV VALUES ('LOCATION','Bathroom');
INSERT INTO EAV VALUES ('LOCATION','courtyard');
INSERT INTO EAV VALUES ('EVENT','verbal aggression');
INSERT INTO EAV VALUES ('EVENT','peer');
INSERT INTO EAV VALUES ('EVENT','bad behavior');
INSERT INTO EAV VALUES ('EVENT','other');


CREATE TABLE EAV_DATA -note lack of constraints, defaults, DRI
(id INTEGER IDENTITY (1,1) NOT NULL,
bts_id INTEGER NULL,
key_col VARCHAR (10) NULL,
attrib_value VARCHAR (50) NULL );


INSERT INTO EAV_DATA VALUES (1, 'LOCATION', 'Bedroom');
INSERT INTO EAV_DATA VALUES (1, 'EVENT', 'other');
INSERT INTO EAV_DATA VALUES (1, 'EVENT', 'bad behavior');
INSERT INTO EAV_DATA VALUES (2, 'LOCATION', 'Bedroom');
INSERT INTO EAV_DATA VALUES (2, 'EVENT', 'other');
INSERT INTO EAV_DATA VALUES (2, 'EVENT', 'verbal aggression');
INSERT INTO EAV_DATA VALUES (3, 'LOCATION', 'courtyard');
INSERT INTO EAV_DATA VALUES (3, 'EVENT', 'other');
INSERT INTO EAV_DATA VALUES (3, 'EVENT', 'peer');


Ideally, the result set of the query would be Location Event count
(headings if possible)


Bedroom verbal aggression 1
Bedroom peer 0
Bedroom bad behavior 0
Bedroom other 2
Dining Room verbal aggression 0
Dining Room peer 0
Dining Room bad behavior 0
Dining Room other 0
Bathroom verbal aggression 0
Bathroom peer 0
Bathroom bad behavior 0
Bathroom other 0
courtyard verbal aggression 0
courtyard peer 1
courtyard bad behavior 0
courtyard other 1


Also, if possible, another query would return this result set. (I think
I know how to do this one.)


Location Event count
Bedroom verbal aggression 1
Bedroom other 2
courtyard peer 1
courtyard other 1


Here is an answer from Thomas Coleman


SELECT Locations.locationvalue, Events.eventvalue,
(SELECT COUNT(*)
FROM (SELECT LocationData.locationvalue, EventData.eventvalue


FROM (SELECT TD1.bts_id, TD1.value AS locationvalue
FROM eav_data AS TD1
WHERE TD1.key = 'location') AS LocationData
INNER JOIN
(SELECT TD2.bts_id, TD2.value AS eventvalue
FROM eav_data AS TD2
WHERE TD2.key = 'event'
) AS EventData
ON LocationData.bts_id = EventData.bts_id
) AS CollatedEventData
WHERE CollatedEventData.locationvalue = Locations.locationvalue
AND CollatedEventData.eventvalue = Events.eventvalue
FROM (SELECT T1.value AS locationvalue
FROM EAV AS T1
WHERE T1.key = 'location') AS Locations,
(SELECT T2.value AS eventvalue
FROM EAV AS T2
WHERE T2.key = 'event') AS Events
ORDER BY Locations.locationvalue, Events.eventvalue ,
SELECT Locations.locationvalue, Events.eventvalue
(SELECT COUNT(*)
FROM (SELECT LocationData.locationvalue, EventData.eventvalue


FROM (SELECT TD1.bts_id, TD1.value AS locationvalue
FROM eav_data AS TD1
WHERE TD1.key = 'location') AS LocationData
INNER JOIN
(SELECT TD2.bts_id, TD2.value AS eventvalue
FROM eav_data AS TD2
WHERE TD2.key = 'event') AS EventData
ON LocationData.bts_id = EventData.bts_id)
AS CollatedEventData
WHERE CollatedEventData.locationvalue = Locations.locationvalue
AND CollatedEventData.eventvalue = Events.eventvalue)
FROM (SELECT T1.value AS locationvalue
FROM EAV AS T1
WHERE T1.key = 'location') AS Locations,
(SELECT T2.value AS eventvalue
FROM EAV AS T2
WHERE T2.key = 'event') AS Events;


Is the same thing in a proper schema as:


SELECT L.locationvalue, E.eventvalue, COUNT(*)
FROM Locations AS L, Events AS E
WHERE L.btd_id = E.btd_id
GROUP BY L.locationvalue, E.eventvalue;


The reason that I had to use so many subqueries is that those entities
are all lopped into the same table. There should be separate tables for
Locations and Events.


The column names are seriously painful; using underscores at the end of
the column name is really non-intuitive. I removed them for my example
and came across the next column name faux pas. Don't use "key" and
"value" for column names. It means that the developer *has* surround
the column name with square brackets for everything which is a serious
pain.


There is such a thing as "too" generic. There has to be some structure
or everything becomes nothing more than a couple of tables called
"things". The real key (no pun intended) is commonality. Is there a
pattern to the data that they want to store? It may not be possible to
create one structure to rule them all and in the darkness bind them.


"To be is to be something in particular; to be nothing in particular is
to be nothing." --Aristole


All data integrity is destroyed. Any typo becomes a new attribute or
entity. Entities are found missing attributes, so all the reports are
wrong.


Try to write a single CHECK() constraint that works for all the
attributes of those 30+ entities your users created because you were
too dumb or too lazy to do your job. It can be done! You need a case
expression almost 70 WHEN clauses for a simple invoice and order system
when I tried it as an exercise.


Try to write a single DEFAULT clause for 30+ entities crammed into one
column. Impossible!


Try to set up DRI actions among the entities. If you thought the WHEN
clauses in the single CASE expression were unmaintainable, wait until
you see the "TRIGGERs from Hell" -- Too bad that they might not fit
into older SQL Server which had some size limits. Now maintain it.


Finally, write a simple relational division query in EAV.