Joining derived tables - mysql

Question

EDIT: I am using phpMyAdmin interface, and I have been copy/paste the codes from phpMyAdmin to here. The phpMyAdmin seems to run a "different code" as I run the following code, and generating some error message that are referring to that "different code", causing huge confusion.
** Final edit: It seems Safari is causing this: it run the "different query" when I try to run 2nd query below. Use Firefox instead, and it generate correct results. Thanks for the help and sorry for the confusion. **
I have two tables: newsFeeds, comments, where
** newsFeeds contains column PID, comments contains column FID.**
I want to join rows in two tables with matching PID = FID. My code is:
SELECT * FROM newsFeeds
INNER JOIN
(
SELECT * FROM
comments
)
ON comments.FID = newsFeeds.PID
and the error message is "#1248 - Every derived table must have its own alias".
I then add in AS newtb after ) according to other posts here. And the code is then:
SELECT * FROM newsFeeds
INNER JOIN
(
SELECT * FROM
comments
) AS newtb
ON newtb.FID = newsFeeds.PID
But another error shows up: #1064 - You have an error in your SQL syntax; check the manual that corresponds to your MySQL server version for the right syntax to use near 'INNER JOIN( SELECTFID,COUNT(*) AScount FROMcomments
LIMIT 0, 25' at line 8
I wonder how to correctly do this?

Answer 1

You should correct this by removing the derived table:
SELECT *
FROM tb_1 INNER JOIN
tb_2
ON tb_2.FID = tb_1.PID;
MySQL has a tendency to materialize derived tables, which hurts performance.
The answer to your question, though, is to add a name after the parentheses:
SELECT *
FROM tb_1 INNER JOIN
(SELECT *
FROM tb_2
) t2
ON t2.FID = tb_1.PID;