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Editorial Team
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Asked: 2026-06-15T07:52:56+00:00

I’m using Postgresql and JDBC and I’m trying to figure out how to create

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I’m using Postgresql and JDBC and I’m trying to figure out how to create an assertion.

I currently have two relations table A(url varchar(30)) and table B(url varchar(30)) and I would like to write an assertion so that it is impossible to insert into table B if that element already exists in table A. How do I do this in JDBC? If it’s not possible to use assertions, how would I make something similar happen?

EDIT: Ok, so I’ve read that it’s not possible to create an assertion using postgresql; thus, my question is now, how would I do something similar using the constraints of Postgresql and JDBC?

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  1. Editorial Team

    What you want is effectively a negative foreign key constraint, which isn’t directly supported. You can implement this constraint using a PL/PgSQL BEFORE INSERT OR UPDATE trigger function that tests the condition.

    See PL/PgSQL trigger procedures in the Pg docs.

    You’ll probably need to use SERIALIZABLE isolation mode to handle races where one transaction inserts into B while the other inserts into A. You’ll need the improved serializable isolation support in 9.1/9.2.

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