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Fix handling of generated columns in ALTER TABLE.

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ALTER TABLE failed if a column referenced in a GENERATED expression
had been added or changed in type earlier in the ALTER command.
That's because the GENERATED expression needs to be evaluated
against the table's updated tuples, but it was being evaluated
against the original tuples.  (Fortunately the executor has adequate
cross-checks to notice the mismatch, so we just got an obscure error
message and not anything more dangerous.)

Per report from Andreas Joseph Krogh.  Back-patch to v12 where
GENERATED was added.

Discussion: https://postgr.es/m/VisenaEmail.200.231b0a41523275d0.16ea7f800c7@tc7-visena
This commit is contained in:
Tom Lane 2020-01-08 09:42:53 -05:00
parent 30a3e772b4
commit 4ac8aaa36f
3 changed files with 132 additions and 29 deletions
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33
src/backend/commands/tablecmds.c
View File

@ -192,13 +192,15 @@ typedef struct NewConstraint
* Phase 3 copy (this could be either a new column with a non-null default, or
* a column that we're changing the type of). Columns without such an entry
* are just copied from the old table during ATRewriteTable. Note that the
* expr is an expression over *old* table values.
* expr is an expression over *old* table values, except when is_generated
* is true; then it is an expression over columns of the *new* tuple.
*/
typedef struct NewColumnValue
{
AttrNumber attnum; /* which column */
Expr *expr; /* expression to compute */
ExprState *exprstate; /* execution state */
bool is_generated; /* is it a GENERATED expression? */
} NewColumnValue;
/*
@ -4961,7 +4963,9 @@ ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap, LOCKMODE lockmode)
/*
* Process supplied expressions to replace selected columns.
* Expression inputs come from the old tuple.
*
* First, evaluate expressions whose inputs come from the old
* tuple.
*/
econtext->ecxt_scantuple = oldslot;
@ -4969,6 +4973,9 @@ ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap, LOCKMODE lockmode)
{
NewColumnValue *ex = lfirst(l);
if (ex->is_generated)
continue;
newslot->tts_values[ex->attnum - 1]
= ExecEvalExpr(ex->exprstate,
econtext,
@ -4977,6 +4984,26 @@ ATRewriteTable(AlteredTableInfo *tab, Oid OIDNewHeap, LOCKMODE lockmode)
ExecStoreVirtualTuple(newslot);
/*
* Now, evaluate any expressions whose inputs come from the
* new tuple. We assume these columns won't reference each
* other, so that there's no ordering dependency.
*/
econtext->ecxt_scantuple = newslot;
foreach(l, tab->newvals)
{
NewColumnValue *ex = lfirst(l);
if (!ex->is_generated)
continue;
newslot->tts_values[ex->attnum - 1]
= ExecEvalExpr(ex->exprstate,
econtext,
&newslot->tts_isnull[ex->attnum - 1]);
}
/*
* Constraints might reference the tableoid column, so
* initialize t_tableOid before evaluating them.
@ -5892,6 +5919,7 @@ ATExecAddColumn(List **wqueue, AlteredTableInfo *tab, Relation rel,
newval = (NewColumnValue *) palloc0(sizeof(NewColumnValue));
newval->attnum = attribute.attnum;
newval->expr = expression_planner(defval);
newval->is_generated = (colDef->generated != '\0');
tab->newvals = lappend(tab->newvals, newval);
}
@ -10379,6 +10407,7 @@ ATPrepAlterColumnType(List **wqueue,
newval = (NewColumnValue *) palloc0(sizeof(NewColumnValue));
newval->attnum = attnum;
newval->expr = (Expr *) transform;
newval->is_generated = false;
tab->newvals = lappend(tab->newvals, newval);
if (ATColumnChangeRequiresRewrite(transform, attnum))

97
src/test/regress/expected/generated.out
View File

@ -593,40 +593,95 @@ ERROR: cannot use generated column "b" in column generation expression
DETAIL: A generated column cannot reference another generated column.
ALTER TABLE gtest25 ADD COLUMN x int GENERATED ALWAYS AS (z * 4) STORED; -- error
ERROR: column "z" does not exist
ALTER TABLE gtest25 ADD COLUMN c int DEFAULT 42,
ADD COLUMN x int GENERATED ALWAYS AS (c * 4) STORED;
ALTER TABLE gtest25 ADD COLUMN d int DEFAULT 101;
ALTER TABLE gtest25 ALTER COLUMN d SET DATA TYPE float8,
ADD COLUMN y float8 GENERATED ALWAYS AS (d * 4) STORED;
SELECT * FROM gtest25 ORDER BY a;
a | b | c | x | d | y
---+----+----+-----+-----+-----
3 | 9 | 42 | 168 | 101 | 404
4 | 12 | 42 | 168 | 101 | 404
(2 rows)
\d gtest25
Table "public.gtest25"
Column | Type | Collation | Nullable | Default
--------+------------------+-----------+----------+------------------------------------------------------
a | integer | | not null |
b | integer | | | generated always as (a * 3) stored
c | integer | | | 42
x | integer | | | generated always as (c * 4) stored
d | double precision | | | 101
y | double precision | | | generated always as (d * 4::double precision) stored
Indexes:
"gtest25_pkey" PRIMARY KEY, btree (a)
-- ALTER TABLE ... ALTER COLUMN
CREATE TABLE gtest27 (
a int,
b int GENERATED ALWAYS AS (a * 2) STORED
b int,
x int GENERATED ALWAYS AS ((a + b) * 2) STORED
);
INSERT INTO gtest27 (a) VALUES (3), (4);
INSERT INTO gtest27 (a, b) VALUES (3, 7), (4, 11);
ALTER TABLE gtest27 ALTER COLUMN a TYPE text; -- error
ERROR: cannot alter type of a column used by a generated column
DETAIL: Column "a" is used by generated column "b".
ALTER TABLE gtest27 ALTER COLUMN b TYPE numeric;
DETAIL: Column "a" is used by generated column "x".
ALTER TABLE gtest27 ALTER COLUMN x TYPE numeric;
\d gtest27
Table "public.gtest27"
Column | Type | Collation | Nullable | Default
--------+---------+-----------+----------+--------------------------------------
Table "public.gtest27"
Column | Type | Collation | Nullable | Default
--------+---------+-----------+----------+--------------------------------------------
a | integer | | |
b | numeric | | | generated always as ((a * 2)) stored
b | integer | | |
x | numeric | | | generated always as (((a + b) * 2)) stored
SELECT * FROM gtest27;
a | b
---+---
3 | 6
4 | 8
a | b | x
---+----+----
3 | 7 | 20
4 | 11 | 30
(2 rows)
ALTER TABLE gtest27 ALTER COLUMN b TYPE boolean USING b <> 0; -- error
ERROR: generation expression for column "b" cannot be cast automatically to type boolean
ALTER TABLE gtest27 ALTER COLUMN b DROP DEFAULT; -- error
ERROR: column "b" of relation "gtest27" is a generated column
ALTER TABLE gtest27 ALTER COLUMN x TYPE boolean USING x <> 0; -- error
ERROR: generation expression for column "x" cannot be cast automatically to type boolean
ALTER TABLE gtest27 ALTER COLUMN x DROP DEFAULT; -- error
ERROR: column "x" of relation "gtest27" is a generated column
-- It's possible to alter the column types this way:
ALTER TABLE gtest27
DROP COLUMN x,
ALTER COLUMN a TYPE bigint,
ALTER COLUMN b TYPE bigint,
ADD COLUMN x bigint GENERATED ALWAYS AS ((a + b) * 2) STORED;
\d gtest27
Table "public.gtest27"
Column | Type | Collation | Nullable | Default
--------+---------+-----------+----------+--------------------------------------
a | integer | | |
b | numeric | | | generated always as ((a * 2)) stored
Table "public.gtest27"
Column | Type | Collation | Nullable | Default
--------+--------+-----------+----------+------------------------------------------
a | bigint | | |
b | bigint | | |
x | bigint | | | generated always as ((a + b) * 2) stored
-- Ideally you could just do this, but not today (and should x change type?):
ALTER TABLE gtest27
ALTER COLUMN a TYPE float8,
ALTER COLUMN b TYPE float8; -- error
ERROR: cannot alter type of a column used by a generated column
DETAIL: Column "a" is used by generated column "x".
\d gtest27
Table "public.gtest27"
Column | Type | Collation | Nullable | Default
--------+--------+-----------+----------+------------------------------------------
a | bigint | | |
b | bigint | | |
x | bigint | | | generated always as ((a + b) * 2) stored
SELECT * FROM gtest27;
a | b | x
---+----+----
3 | 7 | 20
4 | 11 | 30
(2 rows)
-- triggers
CREATE TABLE gtest26 (

31
src/test/regress/sql/generated.sql
View File

@ -316,21 +316,40 @@ ALTER TABLE gtest25 ADD COLUMN b int GENERATED ALWAYS AS (a * 3) STORED;
SELECT * FROM gtest25 ORDER BY a;
ALTER TABLE gtest25 ADD COLUMN x int GENERATED ALWAYS AS (b * 4) STORED; -- error
ALTER TABLE gtest25 ADD COLUMN x int GENERATED ALWAYS AS (z * 4) STORED; -- error
ALTER TABLE gtest25 ADD COLUMN c int DEFAULT 42,
ADD COLUMN x int GENERATED ALWAYS AS (c * 4) STORED;
ALTER TABLE gtest25 ADD COLUMN d int DEFAULT 101;
ALTER TABLE gtest25 ALTER COLUMN d SET DATA TYPE float8,
ADD COLUMN y float8 GENERATED ALWAYS AS (d * 4) STORED;
SELECT * FROM gtest25 ORDER BY a;
\d gtest25
-- ALTER TABLE ... ALTER COLUMN
CREATE TABLE gtest27 (
a int,
b int GENERATED ALWAYS AS (a * 2) STORED
b int,
x int GENERATED ALWAYS AS ((a + b) * 2) STORED
);
INSERT INTO gtest27 (a) VALUES (3), (4);
INSERT INTO gtest27 (a, b) VALUES (3, 7), (4, 11);
ALTER TABLE gtest27 ALTER COLUMN a TYPE text; -- error
ALTER TABLE gtest27 ALTER COLUMN b TYPE numeric;
ALTER TABLE gtest27 ALTER COLUMN x TYPE numeric;
\d gtest27
SELECT * FROM gtest27;
ALTER TABLE gtest27 ALTER COLUMN b TYPE boolean USING b <> 0; -- error
ALTER TABLE gtest27 ALTER COLUMN b DROP DEFAULT; -- error
ALTER TABLE gtest27 ALTER COLUMN x TYPE boolean USING x <> 0; -- error
ALTER TABLE gtest27 ALTER COLUMN x DROP DEFAULT; -- error
-- It's possible to alter the column types this way:
ALTER TABLE gtest27
DROP COLUMN x,
ALTER COLUMN a TYPE bigint,
ALTER COLUMN b TYPE bigint,
ADD COLUMN x bigint GENERATED ALWAYS AS ((a + b) * 2) STORED;
\d gtest27
-- Ideally you could just do this, but not today (and should x change type?):
ALTER TABLE gtest27
ALTER COLUMN a TYPE float8,
ALTER COLUMN b TYPE float8; -- error
\d gtest27
SELECT * FROM gtest27;
-- triggers
CREATE TABLE gtest26 (