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Disallow whole-row variables in GENERATED expressions.

2021年5月21日 19:12:08 +0000 (15:12 -0400)

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

src/backend/catalog/heap.c patch | blob | blame | history

src/test/regress/expected/generated.out patch | blob | blame | history

src/test/regress/sql/generated.sql patch | blob | blame | history

diff --git a/src/backend/catalog/heap.c b/src/backend/catalog/heap.c

index 431e62e3897269e5fe7af84ab0a9a96f86f722df..ba3e1ecf459bde2b74cf1b6076a6b1504dd0648a 100644 (file)

--- a/src/backend/catalog/heap.c

+++ b/src/backend/catalog/heap.c

@@ -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;

}

diff --git a/src/test/regress/expected/generated.out b/src/test/regress/expected/generated.out

index 71542e95d5f0a6453270ae215bbbee8fb027ce79..c2e5676196b1ab6bdf7e5a5fc1facce42f399fc7 100644 (file)

--- a/src/test/regress/expected/generated.out

+++ b/src/test/regress/expected/generated.out

@@ -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

diff --git a/src/test/regress/sql/generated.sql b/src/test/regress/sql/generated.sql

index 914197608b749b39774666a2a8fb4a8e71fd5562..b7eb072671e3cbbd1c218b3d68f2389a8b4ef71f 100644 (file)

--- a/src/test/regress/sql/generated.sql

+++ b/src/test/regress/sql/generated.sql

@@ -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);

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