Question

I’m having an issue with a query that currently uses

LEFT JOIN weblog_data AS pwd    ON (pwd.field_id_41 != ''    AND pwd.field_id_41 LIKE CONCAT('%', ewd.field_id_32, '%')) 

However I’m discovering that I need it to only use that if there is no exact match first. What’s happening is that the query is double dipping due to the use of LIKE, so if it tests for an exact match first then it will avoid the double dipping issue. Can anyone provide me with any further guidance?

Answer 1

It sounds like you want to join the tables aliased as pwd and ewd in your snippet based first on an exact match, and if that fails, then on the like comparison you have now.

Try this:

LEFT JOIN weblog_data AS pwd1 ON (pwd.field_id_41 != '' AND pwd.field_id_41 = ewd.field_id_32) LEFT JOIN weblog_data AS pwd2 ON (pwd.field_id_41 != '' AND pwd.field_id_41 LIKE CONCAT('%', ewd.field_id_32, '%')) 

Then, in your select clause, use something like this:

select   isnull(pwd1.field, pwd2.field) 

however, if you are dealing with a field that can be null in pwd, that will cause problems, this should work though:

select   case pwd1.nonnullfield is null then pwd2.field else pwd1.field end 

You’ll also have to make sure to do a group by, as the join to pwd2 will still add rows to your result set, even if you end up ignoring the data in it.