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Add IF NOT EXISTS processing to ALTER TABLE ADD COLUMN
Fabrízio de Royes Mello, reviewed by Payal Singh, Alvaro Herrera and Michael Paquier.
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+182
-18
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5 files changed

+182
-18
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‎doc/src/sgml/ref/alter_table.sgml‎

Lines changed: 5 additions & 3 deletions
Original file line numberDiff line numberDiff line change
@@ -36,7 +36,7 @@ ALTER TABLE ALL IN TABLESPACE <replaceable class="PARAMETER">name</replaceable>
3636

3737
<phrase>where <replaceable class="PARAMETER">action</replaceable> is one of:</phrase>
3838

39-
ADD [ COLUMN ] <replaceable class="PARAMETER">column_name</replaceable> <replaceable class="PARAMETER">data_type</replaceable> [ COLLATE <replaceable class="PARAMETER">collation</replaceable> ] [ <replaceable class="PARAMETER">column_constraint</replaceable> [ ... ] ]
39+
ADD [ COLUMN ] [ IF NOT EXISTS ] <replaceable class="PARAMETER">column_name</replaceable> <replaceable class="PARAMETER">data_type</replaceable> [ COLLATE <replaceable class="PARAMETER">collation</replaceable> ] [ <replaceable class="PARAMETER">column_constraint</replaceable> [ ... ] ]
4040
DROP [ COLUMN ] [ IF EXISTS ] <replaceable class="PARAMETER">column_name</replaceable> [ RESTRICT | CASCADE ]
4141
ALTER [ COLUMN ] <replaceable class="PARAMETER">column_name</replaceable> [ SET DATA ] TYPE <replaceable class="PARAMETER">data_type</replaceable> [ COLLATE <replaceable class="PARAMETER">collation</replaceable> ] [ USING <replaceable class="PARAMETER">expression</replaceable> ]
4242
ALTER [ COLUMN ] <replaceable class="PARAMETER">column_name</replaceable> SET DEFAULT <replaceable class="PARAMETER">expression</replaceable>
@@ -96,11 +96,13 @@ ALTER TABLE ALL IN TABLESPACE <replaceable class="PARAMETER">name</replaceable>
9696

9797
<variablelist>
9898
<varlistentry>
99-
<term><literal>ADD COLUMN</literal></term>
99+
<term><literal>ADD COLUMN [ IF NOT EXISTS ]</literal></term>
100100
<listitem>
101101
<para>
102102
This form adds a new column to the table, using the same syntax as
103-
<xref linkend="SQL-CREATETABLE">.
103+
<xref linkend="SQL-CREATETABLE">. If <literal>IF NOT EXISTS</literal>
104+
is specified and a column already exists with this name,
105+
no error is thrown.
104106
</para>
105107
</listitem>
106108
</varlistentry>

‎src/backend/commands/tablecmds.c‎

Lines changed: 37 additions & 15 deletions
Original file line numberDiff line numberDiff line change
@@ -328,8 +328,9 @@ static void ATPrepAddColumn(List **wqueue, Relation rel, bool recurse, bool recu
328328
bool is_view, AlterTableCmd *cmd, LOCKMODE lockmode);
329329
static ObjectAddress ATExecAddColumn(List **wqueue, AlteredTableInfo *tab,
330330
Relation rel, ColumnDef *colDef, bool isOid,
331-
bool recurse, bool recursing, LOCKMODE lockmode);
332-
static void check_for_column_name_collision(Relation rel, const char *colname);
331+
bool recurse, bool recursing, bool if_not_exists, LOCKMODE lockmode);
332+
static bool check_for_column_name_collision(Relation rel, const char *colname,
333+
bool if_not_exists);
333334
static void add_column_datatype_dependency(Oid relid, int32 attnum, Oid typid);
334335
static void add_column_collation_dependency(Oid relid, int32 attnum, Oid collid);
335336
static void ATPrepAddOids(List **wqueue, Relation rel, bool recurse,
@@ -2304,7 +2305,7 @@ renameatt_internal(Oid myrelid,
23042305
oldattname)));
23052306

23062307
/* new name should not already exist */
2307-
check_for_column_name_collision(targetrelation, newattname);
2308+
(void) check_for_column_name_collision(targetrelation, newattname, false);
23082309

23092310
/* apply the update */
23102311
namestrcpy(&(attform->attname), newattname);
@@ -3455,11 +3456,11 @@ ATExecCmd(List **wqueue, AlteredTableInfo *tab, Relation rel,
34553456
case AT_AddColumnToView: /* add column via CREATE OR REPLACE
34563457
* VIEW */
34573458
address = ATExecAddColumn(wqueue, tab, rel, (ColumnDef *) cmd->def,
3458-
false, false, false, lockmode);
3459+
false, false, false, false, lockmode);
34593460
break;
34603461
case AT_AddColumnRecurse:
34613462
address = ATExecAddColumn(wqueue, tab, rel, (ColumnDef *) cmd->def,
3462-
false, true, false, lockmode);
3463+
false, true, false, cmd->missing_ok, lockmode);
34633464
break;
34643465
case AT_ColumnDefault: /* ALTER COLUMN DEFAULT */
34653466
address = ATExecColumnDefault(rel, cmd->name, cmd->def, lockmode);
@@ -3572,14 +3573,14 @@ ATExecCmd(List **wqueue, AlteredTableInfo *tab, Relation rel,
35723573
if (cmd->def != NULL)
35733574
address =
35743575
ATExecAddColumn(wqueue, tab, rel, (ColumnDef *) cmd->def,
3575-
true, false, false, lockmode);
3576+
true, false, false, cmd->missing_ok, lockmode);
35763577
break;
35773578
case AT_AddOidsRecurse: /* SET WITH OIDS */
35783579
/* Use the ADD COLUMN code, unless prep decided to do nothing */
35793580
if (cmd->def != NULL)
35803581
address =
35813582
ATExecAddColumn(wqueue, tab, rel, (ColumnDef *) cmd->def,
3582-
true, true, false, lockmode);
3583+
true, true, false, cmd->missing_ok, lockmode);
35833584
break;
35843585
case AT_DropOids: /* SET WITHOUT OIDS */
35853586

@@ -4677,7 +4678,7 @@ ATPrepAddColumn(List **wqueue, Relation rel, bool recurse, bool recursing,
46774678
static ObjectAddress
46784679
ATExecAddColumn(List **wqueue, AlteredTableInfo *tab, Relation rel,
46794680
ColumnDef *colDef, bool isOid,
4680-
bool recurse, bool recursing, LOCKMODE lockmode)
4681+
bool recurse, bool recursing, bool if_not_exists, LOCKMODE lockmode)
46814682
{
46824683
Oid myrelid = RelationGetRelid(rel);
46834684
Relation pgclass,
@@ -4771,8 +4772,14 @@ ATExecAddColumn(List **wqueue, AlteredTableInfo *tab, Relation rel,
47714772
elog(ERROR, "cache lookup failed for relation %u", myrelid);
47724773
relkind = ((Form_pg_class) GETSTRUCT(reltup))->relkind;
47734774

4774-
/* new name should not already exist */
4775-
check_for_column_name_collision(rel, colDef->colname);
4775+
/* skip if the name already exists and if_not_exists is true */
4776+
if (!check_for_column_name_collision(rel, colDef->colname, if_not_exists))
4777+
{
4778+
heap_close(attrdesc, RowExclusiveLock);
4779+
heap_freetuple(reltup);
4780+
heap_close(pgclass, RowExclusiveLock);
4781+
return InvalidObjectAddress;
4782+
}
47764783

47774784
/* Determine the new attribute's number */
47784785
if (isOid)
@@ -5002,7 +5009,8 @@ ATExecAddColumn(List **wqueue, AlteredTableInfo *tab, Relation rel,
50025009

50035010
/* Recurse to child; return value is ignored */
50045011
ATExecAddColumn(wqueue, childtab, childrel,
5005-
colDef, isOid, recurse, true, lockmode);
5012+
colDef, isOid, recurse, true,
5013+
if_not_exists, lockmode);
50065014

50075015
heap_close(childrel, NoLock);
50085016
}
@@ -5013,10 +5021,11 @@ ATExecAddColumn(List **wqueue, AlteredTableInfo *tab, Relation rel,
50135021

50145022
/*
50155023
* If a new or renamed column will collide with the name of an existing
5016-
* column, error out.
5024+
* column and if_not_exists is false then error out, else do nothing.
50175025
*/
5018-
static void
5019-
check_for_column_name_collision(Relation rel, const char *colname)
5026+
static bool
5027+
check_for_column_name_collision(Relation rel, const char *colname,
5028+
bool if_not_exists)
50205029
{
50215030
HeapTuple attTuple;
50225031
int attnum;
@@ -5029,7 +5038,7 @@ check_for_column_name_collision(Relation rel, const char *colname)
50295038
ObjectIdGetDatum(RelationGetRelid(rel)),
50305039
PointerGetDatum(colname));
50315040
if (!HeapTupleIsValid(attTuple))
5032-
return;
5041+
return true;
50335042

50345043
attnum = ((Form_pg_attribute) GETSTRUCT(attTuple))->attnum;
50355044
ReleaseSysCache(attTuple);
@@ -5045,10 +5054,23 @@ check_for_column_name_collision(Relation rel, const char *colname)
50455054
errmsg("column name \"%s\" conflicts with a system column name",
50465055
colname)));
50475056
else
5057+
{
5058+
if (if_not_exists)
5059+
{
5060+
ereport(NOTICE,
5061+
(errcode(ERRCODE_DUPLICATE_COLUMN),
5062+
errmsg("column \"%s\" of relation \"%s\" already exists, skipping",
5063+
colname, RelationGetRelationName(rel))));
5064+
return false;
5065+
}
5066+
50485067
ereport(ERROR,
50495068
(errcode(ERRCODE_DUPLICATE_COLUMN),
50505069
errmsg("column \"%s\" of relation \"%s\" already exists",
50515070
colname, RelationGetRelationName(rel))));
5071+
}
5072+
5073+
return true;
50525074
}
50535075

50545076
/*

‎src/backend/parser/gram.y‎

Lines changed: 20 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1942,6 +1942,16 @@ alter_table_cmd:
19421942
AlterTableCmd *n = makeNode(AlterTableCmd);
19431943
n->subtype = AT_AddColumn;
19441944
n->def = $2;
1945+
n->missing_ok = false;
1946+
$$ = (Node *)n;
1947+
}
1948+
/* ALTER TABLE <name> ADD IF NOT EXISTS <coldef> */
1949+
| ADD_P IF_P NOT EXISTS columnDef
1950+
{
1951+
AlterTableCmd *n = makeNode(AlterTableCmd);
1952+
n->subtype = AT_AddColumn;
1953+
n->def = $5;
1954+
n->missing_ok = true;
19451955
$$ = (Node *)n;
19461956
}
19471957
/* ALTER TABLE <name> ADD COLUMN <coldef> */
@@ -1950,6 +1960,16 @@ alter_table_cmd:
19501960
AlterTableCmd *n = makeNode(AlterTableCmd);
19511961
n->subtype = AT_AddColumn;
19521962
n->def = $3;
1963+
n->missing_ok = false;
1964+
$$ = (Node *)n;
1965+
}
1966+
/* ALTER TABLE <name> ADD COLUMN IF NOT EXISTS <coldef> */
1967+
| ADD_P COLUMN IF_P NOT EXISTS columnDef
1968+
{
1969+
AlterTableCmd *n = makeNode(AlterTableCmd);
1970+
n->subtype = AT_AddColumn;
1971+
n->def = $6;
1972+
n->missing_ok = true;
19531973
$$ = (Node *)n;
19541974
}
19551975
/* ALTER TABLE <name> ALTER [COLUMN] <colname> {SET DEFAULT <expr>|DROP DEFAULT} */

‎src/test/regress/expected/alter_table.out‎

Lines changed: 89 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -2605,3 +2605,92 @@ ALTER TABLE logged1 SET UNLOGGED; -- silently do nothing
26052605
DROP TABLE logged3;
26062606
DROP TABLE logged2;
26072607
DROP TABLE logged1;
2608+
-- test ADD COLUMN IF NOT EXISTS
2609+
CREATE TABLE test_add_column(c1 integer);
2610+
\d test_add_column
2611+
Table "public.test_add_column"
2612+
Column | Type | Modifiers
2613+
--------+---------+-----------
2614+
c1 | integer |
2615+
2616+
ALTER TABLE test_add_column
2617+
ADD COLUMN c2 integer;
2618+
\d test_add_column
2619+
Table "public.test_add_column"
2620+
Column | Type | Modifiers
2621+
--------+---------+-----------
2622+
c1 | integer |
2623+
c2 | integer |
2624+
2625+
ALTER TABLE test_add_column
2626+
ADD COLUMN c2 integer; -- fail because c2 already exists
2627+
ERROR: column "c2" of relation "test_add_column" already exists
2628+
\d test_add_column
2629+
Table "public.test_add_column"
2630+
Column | Type | Modifiers
2631+
--------+---------+-----------
2632+
c1 | integer |
2633+
c2 | integer |
2634+
2635+
ALTER TABLE test_add_column
2636+
ADD COLUMN IF NOT EXISTS c2 integer; -- skipping because c2 already exists
2637+
NOTICE: column "c2" of relation "test_add_column" already exists, skipping
2638+
\d test_add_column
2639+
Table "public.test_add_column"
2640+
Column | Type | Modifiers
2641+
--------+---------+-----------
2642+
c1 | integer |
2643+
c2 | integer |
2644+
2645+
ALTER TABLE test_add_column
2646+
ADD COLUMN c2 integer, -- fail because c2 already exists
2647+
ADD COLUMN c3 integer;
2648+
ERROR: column "c2" of relation "test_add_column" already exists
2649+
\d test_add_column
2650+
Table "public.test_add_column"
2651+
Column | Type | Modifiers
2652+
--------+---------+-----------
2653+
c1 | integer |
2654+
c2 | integer |
2655+
2656+
ALTER TABLE test_add_column
2657+
ADD COLUMN IF NOT EXISTS c2 integer, -- skipping because c2 already exists
2658+
ADD COLUMN c3 integer; -- fail because c3 already exists
2659+
NOTICE: column "c2" of relation "test_add_column" already exists, skipping
2660+
\d test_add_column
2661+
Table "public.test_add_column"
2662+
Column | Type | Modifiers
2663+
--------+---------+-----------
2664+
c1 | integer |
2665+
c2 | integer |
2666+
c3 | integer |
2667+
2668+
ALTER TABLE test_add_column
2669+
ADD COLUMN IF NOT EXISTS c2 integer, -- skipping because c2 already exists
2670+
ADD COLUMN IF NOT EXISTS c3 integer; -- skipping because c3 already exists
2671+
NOTICE: column "c2" of relation "test_add_column" already exists, skipping
2672+
NOTICE: column "c3" of relation "test_add_column" already exists, skipping
2673+
\d test_add_column
2674+
Table "public.test_add_column"
2675+
Column | Type | Modifiers
2676+
--------+---------+-----------
2677+
c1 | integer |
2678+
c2 | integer |
2679+
c3 | integer |
2680+
2681+
ALTER TABLE test_add_column
2682+
ADD COLUMN IF NOT EXISTS c2 integer, -- skipping because c2 already exists
2683+
ADD COLUMN IF NOT EXISTS c3 integer, -- skipping because c3 already exists
2684+
ADD COLUMN c4 integer;
2685+
NOTICE: column "c2" of relation "test_add_column" already exists, skipping
2686+
NOTICE: column "c3" of relation "test_add_column" already exists, skipping
2687+
\d test_add_column
2688+
Table "public.test_add_column"
2689+
Column | Type | Modifiers
2690+
--------+---------+-----------
2691+
c1 | integer |
2692+
c2 | integer |
2693+
c3 | integer |
2694+
c4 | integer |
2695+
2696+
DROP TABLE test_add_column;

‎src/test/regress/sql/alter_table.sql‎

Lines changed: 31 additions & 0 deletions
Original file line numberDiff line numberDiff line change
@@ -1724,3 +1724,34 @@ ALTER TABLE logged1 SET UNLOGGED; -- silently do nothing
17241724
DROP TABLE logged3;
17251725
DROP TABLE logged2;
17261726
DROP TABLE logged1;
1727+
1728+
-- test ADD COLUMN IF NOT EXISTS
1729+
CREATE TABLE test_add_column(c1 integer);
1730+
\d test_add_column
1731+
ALTER TABLE test_add_column
1732+
ADD COLUMN c2 integer;
1733+
\d test_add_column
1734+
ALTER TABLE test_add_column
1735+
ADD COLUMN c2 integer; -- fail because c2 already exists
1736+
\d test_add_column
1737+
ALTER TABLE test_add_column
1738+
ADD COLUMN IF NOT EXISTS c2 integer; -- skipping because c2 already exists
1739+
\d test_add_column
1740+
ALTER TABLE test_add_column
1741+
ADD COLUMN c2 integer, -- fail because c2 already exists
1742+
ADD COLUMN c3 integer;
1743+
\d test_add_column
1744+
ALTER TABLE test_add_column
1745+
ADD COLUMN IF NOT EXISTS c2 integer, -- skipping because c2 already exists
1746+
ADD COLUMN c3 integer; -- fail because c3 already exists
1747+
\d test_add_column
1748+
ALTER TABLE test_add_column
1749+
ADD COLUMN IF NOT EXISTS c2 integer, -- skipping because c2 already exists
1750+
ADD COLUMN IF NOT EXISTS c3 integer; -- skipping because c3 already exists
1751+
\d test_add_column
1752+
ALTER TABLE test_add_column
1753+
ADD COLUMN IF NOT EXISTS c2 integer, -- skipping because c2 already exists
1754+
ADD COLUMN IF NOT EXISTS c3 integer, -- skipping because c3 already exists
1755+
ADD COLUMN c4 integer;
1756+
\d test_add_column
1757+
DROP TABLE test_add_column;

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