TR: redundant constraint_schema - Mailing list pgsql-hackers

Hi,

Please find a question that didn't get an answer in the pgsql-sql list. I hope I'll get an answer here.

Thanks,

Olivier

Hi,

Can someone explain why, when a column is not created (add column if not exists), a redundant constraint is still created from the REFERENCES part ?

I have a patching script that is supposed to add column if not existing :

ALTER TABLE myschem.table1

          ADD COLUMN IF NOT EXISTS col1 VARCHAR(254) REFERENCES myschem.table2(col2)

When col1 already exists, I expected that nothing would happen. But, when applying the previous query and then querying :

select constraint_name from information_schema.key_column_usage where constraint_schema='myschem'

I notice that a new constraint "table1_col2_fkeyxxx" is created each time the previous ALTER TABLE is called (with xxx being a new number each time)

Thanks,

Olivier