Rob wrote : > > Given a table with some non-unique column theCol, what is the most efficient > way to count the number of different values in theCol? I guess you can use a > temporary table as a subselect: > > CREATE TEMPORARY TABLE tmp SELECT UNIQUE theCol FROM theTable; > SELECT COUNT(*) FROM tmp; > DROP TABLE tmp; > > But this seem obscenely inefficient- it's a situation just screaming out for > a summary function: > > SELECT COUNT_UNIQUE(theCol) FROM theTable; > > Does such a function exist in mySQL? Is one planned? > > Further, using the first method, what are the efficiency and robustness > differences between using 'SELECT UNIQUE theCol' and 'SELECT theCol GROUP BY > theCol'? > Hi,
SELECT COUNT(DISTINCT theCol) FROM theTable; should do it. Regards -- Joseph Bueno NetClub/Trader.com --------------------------------------------------------------------- Before posting, please check: http://www.mysql.com/manual.php (the manual) http://lists.mysql.com/ (the list archive) To request this thread, e-mail <[EMAIL PROTECTED]> To unsubscribe, e-mail <[EMAIL PROTECTED]> Trouble unsubscribing? Try: http://lists.mysql.com/php/unsubscribe.php
