Hi. I searched MySQL manual but I stil don't know how a JOIN works. I would like to avoid diging into sources so I'm posting this mail.
I have two tables: - a HUGE table having a row ID_keywords - a SMALL table with keywords and columns ID_keywords and keyword_name I have to select some rows from a HUGE table that have certain keywords (there can be 10.000 or even more results). I can acomplish this in two ways: 1. SELECT <some_rows_from_h> FROM HUGE h LEFT JOIN SMALL s ON h.ID_keywords=s.ID_keywords WHERE (s.keyword_name='name1') OR (s.keyword_name='name2') OR ... GROUP BY ... 2. First get ID_keywords for <name1>, <name2>,... and then do: SELECT <some_rows> FROM HUGE WHERE (ID_keywords=<returnes_ID1>) OR (ID_keywords=<returnes_ID2>) OR ... GROUP BY ... And now the question: - How does the JOIN works? Does it first get IDs from the second table (SMALL) and then use them for the WHERE clause? - Which query from the above examples will be faster (on my test data I get every time the response that the query finished in 0.0s , but I'm now working only on a small set of data and not on read data which aren't available to me right now)? - Is there some diference if I made a join on a join? E.g.: SELECT <some_rows> FROM table1 LEFT JOIN table2 ON <something> LEFT JOIN table3 ON <something_else> WHERE <blahblah> GROUP BY ... Thanks and regards, Dezo --------------------------------------------------------------------- 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