Question

well i do not know how to use sql union properly .
i have two tables with domains(url) i want to compare table1 with table2 so that i get unique domain from table 2 which is not in table 1.

example

table1

id   domain
1    google.com
2    facebook
3    stackoverflow.com

table2

id   domain
1    youtube.com
2    facebook
3    stackoverflow.com

so i want that i compare both tables and get youtube.com because its not in table1
i used sql union like that

$query="SELECT table1.domain, table2.domain "."FROM table1, table2 "."WHERE table1.domain != table2.domain";
$result = mysql_query($query) or die(mysql_error());
while ($rec = mysql_fetch_array($result))
{
$new_url=$rec["domain"];
}

now i get double results like youtube.com youtube.com
so help whats wrong with my sql statement

Answer 1

You should use

SELECT t2.domain FROM
table2 t2 LEFT JOIN table1 t1
    ON t2.domain = t1.domain
WHERE t1.domain IS NULL