finding if a foreign key is in use

in my app i have a table where the id serves as a foreign key for one or more 
other tables. if i want to delete a row in the table, i currently search the 
other tables where this table is referenced to see if the row is in use - and 
then, if not in use, permit deletion. Now if i want the delete button in my 
app to be disabled whenever a row that is in use is selected, searching the 
database every time would dramatically slow down the app. is there some sql 
query that will immediatly give an answer as to whether the row is in use or 
not?
-- 
regards
kg

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