Update Records in TargetTable from Source Table with Identical Name Records

Question

I'm trying to update TableA with records from TableB but only where there are no records in TableA already existing with the same Name Column value. I have queries that will do that however what I'd like to do is in the cases where a 'matched' record exists but does not have values in Fieldx/y/z the existing record will update. For instance:

• Target Table | Bob | NULL | NULL|
• Source Table | Bob | New York | Doctor

The Target table would not have a new record created since 'Bob' exists but that existing record would have New York and Doctor added since those fields are NULL or empty/

Answer 1

You can do this with the on duplicate key update option to insert. First create a unique index on name, so duplicates are not allowed:

create unique index TargetTable_name on TargetTable(name);

Then:

insert into TargetTable(name, col1, col2)
    select name, col1, col2
    from SourceTable
    on duplicate key update col1 = coalesce(TargetTable.col1, values(col1)),
                            col2 = coalesce(TargetTable.col2, values(col2));