Re: [PATCH] no table rewrite when set column type to constrained domain

On Tue, Aug 26, 2025 at 11:26 AM jian he <jian.universality@gmail.com> wrote:
>
> typedef struct NewColumnValue
> {
>     AttrNumber    attnum;         /* which column */
>     Expr       *expr;                    /* expression to compute */
>     ExprState  *exprstate;         /* execution state */
>     bool        is_generated;       /* is it a GENERATED expression? */
>     bool        scan_only;           /* table scan only */
> } NewColumnValue;

I changed scan_only to need_compute.

+ *
+ * If need_compute is true, we will evaluate the new column value in Phase 3.
+ * Currently, this is only used in ALTER COLUMN SET DATA TYPE
command, where the
+ * column’s data type is being changed to a constrained domain, and all the
+ * domain's constraints are non-volatile. In case table rewrite, we also set it
+ * to true.
  */
 typedef struct NewColumnValue
 {
@@ -238,6 +244,7 @@ typedef struct NewColumnValue
     Expr       *expr;            /* expression to compute */
     ExprState  *exprstate;        /* execution state */
     bool        is_generated;    /* is it a GENERATED expression? */
+    bool        need_compute;    /* compute this new expression in Phase 3 */
 } NewColumnValue;

I use domain over domain for regress tests.
I also constrained the no–table-rewrite behavior to cases where the coercion is
to a domain type and all constraints of the new domain are non-volatile.

Demo:

CREATE DOMAIN domain1 AS INT CHECK(VALUE > 1) NOT NULL;
CREATE DOMAIN domain11 AS domain1 CHECK(VALUE > 1) NOT NULL;
CREATE DOMAIN domain21 AS domain1 CHECK(VALUE > random(min=>10,
max=>10)) NOT NULL;
CREATE DOMAIN domain3 AS INT8;
CREATE TABLE t22(a INT, b INT);
INSERT INTO t22 VALUES(-2, -1);

-- no table rewrite, but fail at domain constraint check
ALTER TABLE t22 ALTER COLUMN a SET DATA TYPE domain11 USING a::domain11;
-- no table rewrite, but fail at domain constraint check
ALTER TABLE t22 ALTER COLUMN b SET DATA TYPE domain11 USING b::domain11;

-- table rewrite
ALTER TABLE t22 ALTER COLUMN a SET DATA TYPE domain21;
ALTER TABLE t22 ALTER COLUMN b SET DATA TYPE domain3;
ALTER TABLE t22 ALTER COLUMN a SET DATA TYPE domain1 USING (a+0)::domain1;



--
jian
https://www.enterprisedb.com