On 16/01/26 08:31, jian he wrote:
On Thu, Jan 15, 2026 at 11:29 PM Matheus Alcantara
<[email protected]> wrote:
+ /*
+ * Find everything that depends on the column (constraints, indexes,
etc),
+ * and record enough information to let us recreate the objects after
+ * rewrite.
+ */
+ RememberAllDependentForRebuilding(tab, AT_SetExpression, rel, attnum,
colName);
+
Perhaps this comments should be updated since we are now collecting
these dependencies for virtual generated columns too that it not require
a table rewrite.
---
I guess we can change it as:
/*
* Find everything that depends on the column (constraints, indexes, etc),
* and record enough information to let us recreate the objects.
*/
RememberAllDependentForRebuilding(tab, AT_SetExpression, rel,
attnum, colName);
It looks good.
I think that it would be good to update the SET EXPRESSION AS
documentation on doc/src/sgml/ref/alter_table.sgml to mention that for
virtual columns the table is not rewritten but a full table scan may
still be needed if the column has check constraints.
In doc/src/sgml/ref/alter_table.sgml, I intended to change it as follows:
<varlistentry id="sql-altertable-desc-set-expression">
<term><literal>SET EXPRESSION AS</literal></term>
<listitem>
<para>
This form replaces the expression of a generated column. Existing data
in a stored generated column is rewritten and all the future changes
will apply the new generation expression.
+ Virtual generated columns do not require a table rewrite.
+ However if the column is part of a <literal>CHECK</literal> constraint
+ expression, the constraint will be rebuilt, requiring a table scan to
+ ensure that existing rows meet the constraint.
</para>
Sounds good.
--
Matheus Alcantara
EDB: https://www.enterprisedb.com
