select uid,
group_concat(if(keyfld=’name’,valfld, ”) SEPARATOR ” ) as name,
group_concat(if(keyfld=’age’,valfld, ”) SEPARATOR ” ) as age,
group_concat(if(keyfld=’iq’,valfld, ”) SEPARATOR ” ) as iq,
group_concat(if(keyfld=’geekfu’,valfld, ”) SEPARATOR ” ) as geekfu
from aarontbl group by uid;

If you want NULL instead of empty string, an extra IF will do, I guess.

I tried to see if one could export the list of columns into an extra table, but there is no way to dynamically change the requested column with MySQL. Unless there is a trick I’ve missed.

=================================

DELIMITER //

CREATE PROCEDURE recreate_view()
BEGIN
DECLARE sql_statement1 TEXT;
DECLARE sql_statement2 TEXT;
DECLARE sql_statement3 TEXT;
DECLARE fld_name VARCHAR(256);
DECLARE done BOOL DEFAULT FALSE;
DECLARE aliasname CHAR(1);
DECLARE aliascnt INTEGER DEFAULT 66;
DECLARE cur CURSOR FOR SELECT DISTINCT keyfld FROM aarontbl;
DECLARE CONTINUE HANDLER FOR sqlstate ‘02000′ SET done = TRUE;
SET sql_statement1 = ‘CREATE OR REPLACE VIEW aaronview (uid’;
SET sql_statement2 = ‘) AS SELECT DISTINCT A.uid’;
SET sql_statement3 = ‘ FROM aarontbl AS A’;
OPEN cur;
keysloop: LOOP
FETCH cur INTO fld_name;
IF done THEN
CLOSE cur;
LEAVE keysloop;
END IF;
SELECT CHAR(aliascnt) INTO aliasname;
SET aliascnt = aliascnt + 1;
SET sql_statement1 = CONCAT(sql_statement1, ‘, ‘, fld_name);
SET sql_statement2 = CONCAT(sql_statement2, ‘, ‘, aliasname, ‘.valfld’, ‘ AS ‘, fld_name);
SET sql_statement3 = CONCAT(sql_statement3, ‘ LEFT JOIN aarontbl AS ‘, aliasname,
‘ ON (A.uid = ‘, aliasname, ‘.uid AND ‘, aliasname, ‘.keyfld = \”, fld_name, ‘\’)');

END LOOP;
SET @x = CONCAT(sql_statement1, sql_statement2, sql_statement3);
PREPARE x from @x;
EXECUTE x;
DROP PREPARE x;
END;

//

DELIMITER ;

CALL recreate_view();

SELECT * FROM aaronview;

INSERT INTO aarontbl(uid, keyfld, valfld) VALUES (2, ‘test’, ‘test’);

CALL recreate_view();

SELECT * FROM aaronview;

=================================

Since MySQL doesn’t allow dynamic SQL in stored procedures or triggers (another reason to use a proper dbms), you can’t attach to aarontbl a TRIGGER firing after an INSERT and calling recreate_view(), so you have to do it yourself before your SELECT query.

I’m sure there are better solutions, which are left as an exercise for the reader

which is as close as you can get, but really isn’t that bad. you just have to parse it at the first colon.

Pretty cool eh?

cheers,
Joel

And Lorenzo’s suggestion gets slower and slowere which every key added.

I guess the awkward way of accessing the data in this case is the price you have to pay for not-so-perfect normalization.

Philip

Is there any way I could add a new value row into aarontbl and then have aaronview dynamically change? Or is that just not a good idea.

INSERT INTO aarontbl (uid, keyfld, valfld) VALUES
(1,’name’,'Aaron’),
(1,’age’,'28′),
(1,’iq’,'50′),
(2,’name’,'John’),
(2,’age’,'17′),
(2,’iq’,'110′),
(2,’geekfu’,'100′);

CREATE VIEW aaronview (uid, name, age, iq, geekfu) AS
SELECT DISTINCT a.uid,
b.valfld AS name,
c.valfld AS age,
d.valfld AS iq,
e.valfld AS geekfu
FROM aarontbl AS a
LEFT JOIN aarontbl AS b ON (a.uid = b.uid AND b.keyfld = ‘name’)
LEFT JOIN aarontbl AS c ON (a.uid = c.uid AND c.keyfld = ‘age’)
LEFT JOIN aarontbl AS d ON (a.uid = d.uid AND d.keyfld = ‘iq’)
LEFT JOIN aarontbl AS e ON (a.uid = e.uid AND e.keyfld = ‘geekfu’);