INSERT... WHERE NOT EXISTS error - php

Question

I have syntax error with my code
$insert = #mysql_query("INSERT INTO topics (t_title, t_desc, t_pic, t_link, t_date,cat_id)
SELECT '$t_title','$t_desc','$t_pic','$t_link','$t_date','$cat_id'
WHERE NOT EXISTS (SELECT t_link
FROM topics
WHERE t_link = $t_link
)
")or die(mysql_error());
This returns an error :
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 'WHERE NOT EXISTS (SELECT t_link FROM topics WHERE t_link = 'showthread.php?t=120' at line 3
I thought that the problem is with t_link = $t_link
But when i replaced it with normal value , the problem persists.
Any help ?

Answer 1

You missed the FROM on first SELECT
SELECT '$t_title','$t_desc','$t_pic','$t_link','$t_date','$cat_id'
# MISSED HERE FROM ???
WHERE NOT EXISTS

Answer 2

Here solution for FROM CLAUSE, please, check as solution chumkiu's answer, not mine.
create table a ( i int);
insert into a (i )
select 1
from dual
where 1=2;
insert into a (i )
select 3
from dual
where 1=1;
Results

Answer 3

If t_link is has a unique index in the table, you can do:
$insert = #mysql_query("INSERT IGNORE INTO topics (t_title, t_desc, t_pic, t_link, t_date,cat_id)
VALUES ('$t_title','$t_desc','$t_pic','$t_link','$t_date','$cat_id');
The IGNORE keyword tells it to do nothing if the insert would duplicate a unique key constraint.