Commits on Aug 22, 2026
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Support changing a column into a stored generated column
This adds an ALTER TABLE subcommand which turns a regular column into a stored generated column: ... ALTER col ADD GENERATED USING CONSTRAINT constr_name STORED The main purpose of this command is to make it possible to add a stored generated column without rewriting the table under an AccessExclusive lock. Before running this command, the table should have been prepared by adding a regular column, backfilling it with data matching the intended generation expression, and adding the constr_name constraint to prove that the data does satisfy said generation expression. The constraint must have a specific structure to be usable for this operation. If the column is nullable, the constraint must be of the form: CHECK (column_name IS NOT DISTINCT FROM expr) if the column is NOT NULL, either of the following is acceptable: CHECK (column_name IS NOT DISTINCT FROM expr) CHECK (column_name = expr) The column will then be changed into a stored generated column, with the "expr" from the constraint as its generator expression. The operation will be performed without rewriting the table, and without any verification scan. The syntax is chosen for its similarity to: ... ALTER COLUMN ... ADD GENERATED ... AS IDENTITY with the difference that: - since we are not talking about IDENTITY columns, ALWAYS is implicit and does not need to be explicitly supplied - STORED must always be supplied, to make it clear that we are talking about stored and not virtual generated columns (VIRTUAL is the default when omitted in other commands, so we mandate STORED here to be consistent) This new operation fits together with SET EXPRESSION and DROP EXPRESSION: the latter works in the opposite direction, turning a generated column into a regular column. Partitioning/inheritance is supported in the same way as DROP EXPRESSION: it is allowed to change the whole inheritace tree to/from a generated column at once; it is forbidden to change the parent table ONLY and it is forbidden to change a partition directly. See 8bf6ec3 and the associated discussion.
authored and Commitfest Bot committed
Aug 22, 2026
