一次从2张桌子获取信息？

Question

I need to get info from 2 tables in one query, I searched for it on google and it came up with joins? I got this code

mysql_query("SELECT code, url FROM apilinks, links WHERE apilinks.code='$code' and links.code='$code'");

but it doesn't seem to work, it outpus this mysql error

Warning: mysql_num_rows(): supplied argument is not a valid MySQL result resource in /home/codyl/public_html/projects/tests/tirl/code.php on line 18

I need to have it find url and code, in both the links table and the apilinks table, because the url has a get variable, and 'apilinks' is setup differently than 'links' so it will have the same looking url but it has to check both tables

Answer 1

I don't think your error is from your SQL query, but anyway:

Your SQL query generates a cartesian product. Every row in apilinks is joined with every row in links. This is rarely what you want. You need to add a JOIN condition to the WHERE clause.

From your query, I guess code is the column you want to join on.

SELECT links.code, url 
FROM apilinks, links 
WHERE apilinks.code=links.code
AND links.code='$code'

Or with using an explicit join, which may be more obvious to you:

SELECT links.code, url 
FROM apilinks INNER JOIN links ON apilinks.code=links.code
WHERE links.code='$code'