How to find rows in one table that have no corresponding row in another table

Question

I have a 1:1 relationship between two tables. I want to find all the rows in table A that don\'t have a corresponding row in table B. I use this query:

SELEC         


        

Answer 1

select parentTable.id from parentTable
left outer join childTable on (parentTable.id = childTable.parentTableID) 
where childTable.id is null