mysql query select depending on 2 tabels - php

Question

I've reached the php code that I want. But my website is too slow because it keeps repeating and round over and over again,
$pages= mysql_query("SELECT * FROM ex_instagram_p WHERE type = '".follow."' AND active=1 And username !='".$username."' ORDER BY cpc DESC" );
$prow = mysql_fetch_array($pages);
Do{
$dollowed = mysql_query("SELECT * FROM exchanges WHERE user = '".$username."' AND exid = '".$prow['id']."'");
$followed = mysql_num_rows($dollowed);
;}while($followed > 0 && $prow = mysql_fetch_array($pages));
Actually I can explain the code a little more,
I need to choose the maximum CPC row from the first table
But also to make sure that:
type = '".follow."' AND active=1 And username !='".$username."' ORDER BY cpc DESC"
And here comes the problem,
before continue I need to make sure that the 'id' field form the first table does't got a record on the second table with the user username,
is it got result it'll repeat again using the next row,
over and over until finding a result that satisfies both tables.
This method is soooo heavy
I hope to get a simpler and lighter way, thanks
I've tried to do this but it does not work
$prow= mysql_query("SELECT *
FROM (mysql_query("SELECT * FROM ex_instagram_p WHERE type = '".follow."' AND active=1
And username !='".$username."' ORDER BY cpc DESC" );)
INNER JOIN (mysql_query("SELECT * FROM exchanges WHERE user = '".$username."'");)
ON ex_instagram_p.id=exchanges.exid";);

Answer 1

You can do this in one query. It is a bit hard to follow the logic, but I think this is the query that you want:
SELECT i.*
FROM ex_instagram_p i join
exchanges e
on i.id = e.exid
WHERE i.type = '".follow."' AND i.active=1 And
i.username <> '".$username."' and e.user = '".$username."'
ORDER BY i.cpc DESC
LIMIT 1;
Doing the work in the database is generally much faster than cycling through rows in the application. After all, that is what databases are good for -- managing and querying large amounts of data.