Thread: Duplicate values when using same sequence to generate columns across two different tables
Duplicate values when using same sequence to generate columns across two different tables
From
Aditya Rastogi
Date:
Hi,
I am using the same sequence to auto-generate values for columns in two different tables. If multiple parallel sessions are inserting values in either of the tables, is there a chance that there might occur entries with the same integer in the two tables or in one of the tables ?
Thanks in advance,
Aditya
Re: Duplicate values when using same sequence to generate columns across two different tables
From
Thomas Kellerer
Date:
Aditya Rastogi, 27.11.2013 10:00: > I am using the same sequence to auto-generate values for columns in > two different tables. If multiple parallel sessions are inserting > values in either of the tables, is there a chance that there might > occur entries with the same integer in the two tables or in one of > the tables? No, absolutely not.
Re: Duplicate values when using same sequence to generate columns across two different tables
From
David Johnston
Date:
Thomas Kellerer wrote > Aditya Rastogi, 27.11.2013 10:00: >> I am using the same sequence to auto-generate values for columns in >> two different tables. If multiple parallel sessions are inserting >> values in either of the tables, is there a chance that there might >> occur entries with the same integer in the two tables or in one of >> the tables? > > No, absolutely not. While strictly true usually duplicates within a table are prevented via a unique index on the serial column - but that doesn't work in this case - though it will prevent duplicates in the same table. The problem is that even if you define a sequence and use it as a default it is possible for someone to manually specify a value instead - ignoring, and skipping the use of, the sequence. That may or may not be a concern but it can happen and in absence of a constraint preventing such you could end up with cross-table-duplicates. David J. -- View this message in context: http://postgresql.1045698.n5.nabble.com/Duplicate-values-when-using-same-sequence-to-generate-columns-across-two-different-tables-tp5780509p5780603.html Sent from the PostgreSQL - novice mailing list archive at Nabble.com.