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help / color / mirror / Atom feedFrom: Mauricio Martini <[email protected]>
To: [email protected] <[email protected]>
Subject: Technical validation on altering atttypmod for numeric column in PostgreSQL
Date: Mon, 23 Mar 2026 13:02:42 +0000
Message-ID: <BN7PR10MB2609BBFDA87D4BBC22ABF14D824BA@BN7PR10MB2609.namprd10.prod.outlook.com> (raw)
Hi team,
I am evaluating an approach to change the scale of a numeric column from numeric(18,2) to numeric(18,4) in a large table, aiming to avoid the cost of a full table rewrite.
The proposed approach involves directly updating the PostgreSQL system catalog:
UPDATE pg_attribute
SET atttypmod = (18 << 16 | 4) + 4
WHERE attrelid = 'table'::regclass
AND attname = 'column';
Before considering this in practice, I would like to validate a few points:
* Is this approach considered safe from a data integrity perspective?
* Is there a risk of inconsistencies in the internal representation of the numeric type (especially regarding scale)?
* Could this impact indexes, functions, or aggregation operations?
* Is there any official recommendation or prior experience using this approach in production environments?
* Are there additional risks related to rollback, maintenance, or future operations (e.g., dump/restore, upgrades)?
The goal is to determine whether this alternative is viable, or if we should stick with more standard approaches (e.g., shadow column, incremental migration, etc.).
If anyone has experience with a similar scenario, your insights would be appreciated.
Thanks.
Att. Mauricio Martini
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