Optimizing Small MySQL Join Query - php

Question

I have a list of venues in the Venues table, and a list of a cities/states in the Locations table. The venue is associated with an area code unique to my organization, referred to as a SOYID. The SOYID is made up of a geographical area - each row in the Locations table has a City, State, and the corresponding SOYID. Some Venues rows have a SOYID, others do not; for those that do not, I need to find the SOYID for the city and state listed. I only want to select those Venues in a specific SOYID.
This query works, however, it takes a few seconds to load; I don't think I am writing the query correctly. Currently Venues has approx 140 rows, Locations has 40,000.
$sql = "SELECT DISTINCT a.VenueID, a.Name, a.PhotoID, a.City, a.StateAbbr
FROM Venues AS a LEFT JOIN Locations AS c ON a.City = c.city
WHERE a.SOYID = '" . mysql_real_escape_string($SOYID) . "'
OR ((c.city = a.City) AND (c.state = a.StateAbbr) AND (c.SOYID = '" . mysql_real_escape_string($SOYID) . "'))
ORDER BY a.Name ASC";

Answer 1

Any time you reference a column from a LEFT JOINed table (c.state and c.SOYID in your specific case) in the WHERE clause, you force that join to behave like an INNER JOIN. Instead, make those tests part of the join condition:
"SELECT DISTINCT a.VenueID, a.Name, a.PhotoID, a.City, a.StateAbbr
FROM Venues AS a
LEFT JOIN Locations AS c
ON a.City = c.city
AND a.StateAbbr = c.state
AND c.SOYID = '" . mysql_real_escape_string($SOYID) . "'
WHERE a.SOYID = '" . mysql_real_escape_string($SOYID) . "'
OR c.SOYID IS NOT NULL /* LEFT JOIN found a matching row */
ORDER BY a.Name ASC"
EDIT: Based on comments, this version should allow you do remove the DISTINCT requirement:
"SELECT a.VenueID, a.Name, a.PhotoID, a.City, a.StateAbbr
FROM Venues AS a
WHERE a.SOYID = '" . mysql_real_escape_string($SOYID) . "'
OR EXISTS(SELECT NULL
FROM Locations AS c
WHERE a.City = c.city
AND a.StateAbbr = c.state
AND c.SOYID = '" . mysql_real_escape_string($SOYID) . "')
ORDER BY a.Name ASC"