Question

I have the following query:

SELECT * FROM a WHERE
     cityid IN (SELECT id FROM b)
  OR regionid IN (SELECT id FROM b)
  OR countryid IN (SELECT id FROM b)

Is there a way (using MySQL syntax) to avoid running the sub-query 3 times?

Answer 1

Instead of using subselects a join might be used

SELECT a.* FROM a 
   LEFT OUTER JOIN b 
       ON (a.cityid = b.id OR a.regionid = b.id or a.countryid = b.id) 
WHERE b.id IS NOT NULL