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Disallow whole-row variables in GENERATED expressions.

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This was previously allowed, but I think that was just an oversight.
It's a clear violation of the rule that a generated column cannot
depend on itself or other generated columns.  Moreover, because the
code was relying on the assumption that no such cross-references
exist, it was pretty easy to crash ALTER TABLE and perhaps other
places.  Even if you managed not to crash, you got quite unstable,
implementation-dependent results.

Per report from Vitaly Ustinov.
Back-patch to v12 where GENERATED came in.

Discussion: https://postgr.es/m/CAM_DEiWR2DPT6U4xb-Ehigozzd3n3G37ZB1+867zbsEVtYoJww@mail.gmail.com
This commit is contained in:
Tom Lane 2021-05-21 15:12:08 -04:00
parent 2b0ee126bb
commit 4b10074453
3 changed files with 23 additions and 2 deletions
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15
src/backend/catalog/heap.c
View File

@ -3020,15 +3020,26 @@ check_nested_generated_walker(Node *node, void *context)
AttrNumber attnum;
relid = rt_fetch(var->varno, pstate->p_rtable)->relid;
if (!OidIsValid(relid))
return false; /* XXX shouldn't we raise an error? */
attnum = var->varattno;
if (OidIsValid(relid) && AttributeNumberIsValid(attnum) && get_attgenerated(relid, attnum))
if (attnum > 0 && get_attgenerated(relid, attnum))
ereport(ERROR,
(errcode(ERRCODE_SYNTAX_ERROR),
(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
errmsg("cannot use generated column \"%s\" in column generation expression",
get_attname(relid, attnum, false)),
errdetail("A generated column cannot reference another generated column."),
parser_errposition(pstate, var->location)));
/* A whole-row Var is necessarily self-referential, so forbid it */
if (attnum == 0)
ereport(ERROR,
(errcode(ERRCODE_INVALID_OBJECT_DEFINITION),
errmsg("cannot use whole-row variable in column generation expression"),
errdetail("This would cause the generated column to depend on its own value."),
parser_errposition(pstate, var->location)));
/* System columns were already checked in the parser */
return false;
}

7
src/test/regress/expected/generated.out
View File

@ -46,6 +46,13 @@ ERROR: cannot use generated column "b" in column generation expression
LINE 1: ...AYS AS (a * 2) STORED, c int GENERATED ALWAYS AS (b * 3) STO...
^
DETAIL: A generated column cannot reference another generated column.
-- a whole-row var is a self-reference on steroids, so disallow that too
CREATE TABLE gtest_err_2c (a int PRIMARY KEY,
b int GENERATED ALWAYS AS (num_nulls(gtest_err_2c)) STORED);
ERROR: cannot use whole-row variable in column generation expression
LINE 2: b int GENERATED ALWAYS AS (num_nulls(gtest_err_2c)) STOR...
^
DETAIL: This would cause the generated column to depend on its own value.
-- invalid reference
CREATE TABLE gtest_err_3 (a int PRIMARY KEY, b int GENERATED ALWAYS AS (c * 2) STORED);
ERROR: column "c" does not exist

3
src/test/regress/sql/generated.sql
View File

@ -17,6 +17,9 @@ CREATE TABLE gtest_err_1 (a int PRIMARY KEY, b int GENERATED ALWAYS AS (a * 2) S
-- references to other generated columns, including self-references
CREATE TABLE gtest_err_2a (a int PRIMARY KEY, b int GENERATED ALWAYS AS (b * 2) STORED);
CREATE TABLE gtest_err_2b (a int PRIMARY KEY, b int GENERATED ALWAYS AS (a * 2) STORED, c int GENERATED ALWAYS AS (b * 3) STORED);
-- a whole-row var is a self-reference on steroids, so disallow that too
CREATE TABLE gtest_err_2c (a int PRIMARY KEY,
b int GENERATED ALWAYS AS (num_nulls(gtest_err_2c)) STORED);
-- invalid reference
CREATE TABLE gtest_err_3 (a int PRIMARY KEY, b int GENERATED ALWAYS AS (c * 2) STORED);