Optimizing query that runs slowly on Linux

[Shaman13]

I was wondering if anyone has any insight into why the query I have posted below runs exceedingly slow on my Linux server. I am using Php with a MySQL database. On both my development computers the query runs briskly. They are however both Windows boxes, one running Windows XP and the other running Windows 2000 Professional. Here is the culprit. Any and all suggestions are welcomed. Thanks! Happy Holidays!

if (!empty($_SESSION['CASENUM'])) {
$result = mysql_query("SELECT * FROM _clientsw left join _clientsw_cases ON _clientsw.CLIENTNUM=_clientsw_cases.CLIENTNUM WHERE CASENUM='{$_SESSION['CASENUM']}'");
list($CLIENTNUM,$PCODE,$CFNAME,$CLNAME,$CADDRESS,$CCITY,$CSTATE,$CZIP,$CACODE,
$CPHONE,$CASETYPE,$DOPEN,$CCOUNTY,$SEX,$AGE,$RACE,$CHILDREN,$ADULTS,$KNOW,
$OFFICENUM,$FUNDSNUM,$SNUM,$PHELPED,$CITIZEN,$CMI,$SSN,$BDATE,$LANGUAGE,$MARITALS,
$SLNAME,$SFNAME,$CSTATUS,$EXT,$LIVEAR,$SERVICE,$IRCLOSED,$UW,$NOTES,$iMonth,$iDay,$iYear,$PAMPHLET)
=mysql_fetch_array($result);

[Birdman]

You may want to check the tables and make sure the indexes are set up the same.

Having indexes on these(CLIENTNUM CASENUM) fields should speed things up.

Also, how large are these tables?

[Shaman13]

Thanks Birdman! That worked slick! It solved my problem. Have a Great Day!