Question

I have 4 tables. Users, Articles, Langs, LangList

Articles table: …, uid (Users.id), lang (Langs.id),…

LangList table: id, uid (Users.id), langid (Langs.id)

I want to select all those articles for a specified user (ex. Users.id = 66), where are in his selected languages list.

If i make this:

function FindActiveLangs($lang){
    $sql ="SELECT langid FROM LangList WHERE `uid`= '66' AND `active`='1';";
    $rsd = mysql_query($sql);
    $lang_string = " ( ".$lang."lang = '0' ";
    while($row = mysql_fetch_array($rsd)){
        $lang_string .= " OR ".$lang."lang = '".$row['langid']."' ";
    }
    $lang_string .= " ) ";
    return $lang_string;
} //end of FindActiveLangs


$tables = " Articles ";
$lang_string = FindActiveLangs("Articles.");
$where1 = "WHERE ".$lang_string." ";
$sql = "select distinct Articles.id, title, descr, thumb, relDate, 
            Articles.alias, Articles.lang, author, source  
        from ".$tables.$where1." and Users";

I took the results in 0.01-0.03 secs

In the second way, that I think is better for clean code:

$sql = "select distinct Articles.id, title, descr, thumb, relDate, 
            Articles.alias, Articles.lang, author, source  
        from Articles 
        where lang IN 
            (SELECT langid FROM LangList WHERE uid= '66' AND active='1')";

I took the results in 1.1-1.3 secs

Is there any way to execute this query, with second way with better performance? the “IN” kills the speed

Thanks in advance…

Answer 1

look at EXISTS instead of IN. The performance is much better.

select distinct Articles.id, title, descr, thumb, relDate, Articles.alias, Articles.lang, author, source  
from Articles, TagsList 
where
    Articles.lang = 0 OR 
    EXISTS 
          (SELECT *
           FROM LangList 
           WHERE uid= '66' AND active='1' 
           AND langid = Articles.lang)

EDIT: second attempt (check if the performance is any better):

SELECT Articles.*
   FROM Articles 
    INNER JOIN LangList
        ON langid = Articles.lang
   WHERE uid= '66' AND active='1' 

UNION

SELECT Articles.*
FROM Articles
WHERE 
Articles.lang=0
AND
NOT EXISTS
(
    SELECT *
           FROM LangList 
           WHERE uid= '66' AND active='1' 
           AND langid = Articles.lang
)