Re: set not null column using existing constraint

[Marco Piovan <mpiovan@xxxxxxxxxxxx>]

The column is not marked as NOT NULL but a valid constraint  "CHECK (column IS NOT NULL)" exists.

I haven't found a way to use that specific constraint and avoid the table rescan.

Regards

On Wed, Jan 10, 2018 at 5:00 PM, Rui DeSousa <rui.desousa@xxxxxxxxxx> wrote:

Marco,

Since the column has already been altered to be not null then attaching the primary key will not need to rescan the table to mark the column as not null again — just use the “using index" clause.  

i.e.

alter table rui.member add primary key using index member_pkey;

On Jan 10, 2018, at 7:09 AM, Marco Piovan <mpiovan@xxxxxxxxxxxx> wrote:

Hello,

I want to create a primary key using  an existing unique index.
I have already created the index concurrently and I have already validated a not null constraint on the same column.

Looking at the postgres documentation (https://www.postgresql.org/docs/9.6/static/sql-altertable.html):

"If PRIMARY KEY is specified, and the index's columns are not already marked NOT NULL, then this command will attempt to do ALTER COLUMN SET NOT NULL against each such column. That requires a full table scan to verify the column(s) contain no nulls. In all other cases, this is a fast operation."

Is it possible to specify the already validated not null constraint and avoid another scan of the table (with lock)?

Best regards

--

Marco Piovan

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Marco Piovan

Senior System Engineer
mpiovan@xxxxxxxxxxxx | workwave.com

Via Luigi Da Porto, 2/C - 37122 Verona (VR) - Italy

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