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Postgres deferred PRIMARY KEYS, a hidden gem

Oracle 7.3 supports it!

That is how this all started. A gentleman tweeted about a Postgres limitation that Oracle has not had since at least since Oracle 7.3

The problem

As you can see in the tweet, Postgres by default will not defer a PRIMARY KEY check. Without the check being deferred the following will not work:

postgres=# select * from demo; 
(2 rows)
postgres=# alter table demo add primary key(id);   
postgres=# begin;
postgres=# update demo set id=id-1;
postgres=# update demo set id=id+1;
ERROR:  duplicate key value violates unique constraint "demo_pkey"
DETAIL:  Key (id)=(1) already exists.


The solution

The solution, as mentioned ...

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