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Add IF NOT EXISTS processing to ALTER TABLE ADD COLUMN
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Fabrízio de Royes Mello, reviewed by Payal Singh, Alvaro Herrera and
Michael Paquier.
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@adunstan
adunstan committed Jul 30, 2015
1 parent 632cd9f commit 2cd40ad
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Showing 5 changed files with 182 additions and 18 deletions.
8 changes: 5 additions & 3 deletions doc/src/sgml/ref/alter_table.sgml
View file
Expand Up @@ -36,7 +36,7 @@ ALTER TABLE ALL IN TABLESPACE <replaceable class="PARAMETER">name</replaceable>

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

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> [ ... ] ]
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> [ ... ] ]
DROP [ COLUMN ] [ IF EXISTS ] <replaceable class="PARAMETER">column_name</replaceable> [ RESTRICT | CASCADE ]
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> ]
ALTER [ COLUMN ] <replaceable class="PARAMETER">column_name</replaceable> SET DEFAULT <replaceable class="PARAMETER">expression</replaceable>
Expand Down Expand Up @@ -96,11 +96,13 @@ ALTER TABLE ALL IN TABLESPACE <replaceable class="PARAMETER">name</replaceable>

<variablelist>
<varlistentry>
<term><literal>ADD COLUMN</literal></term>
<term><literal>ADD COLUMN [ IF NOT EXISTS ]</literal></term>
<listitem>
<para>
This form adds a new column to the table, using the same syntax as
<xref linkend="SQL-CREATETABLE">.
<xref linkend="SQL-CREATETABLE">. If <literal>IF NOT EXISTS</literal>
is specified and a column already exists with this name,
no error is thrown.
</para>
</listitem>
</varlistentry>
Expand Down
52 changes: 37 additions & 15 deletions src/backend/commands/tablecmds.c
View file
Expand Up @@ -328,8 +328,9 @@ static void ATPrepAddColumn(List **wqueue, Relation rel, bool recurse, bool recu
bool is_view, AlterTableCmd *cmd, LOCKMODE lockmode);
static ObjectAddress ATExecAddColumn(List **wqueue, AlteredTableInfo *tab,
Relation rel, ColumnDef *colDef, bool isOid,
bool recurse, bool recursing, LOCKMODE lockmode);
static void check_for_column_name_collision(Relation rel, const char *colname);
bool recurse, bool recursing, bool if_not_exists, LOCKMODE lockmode);
static bool check_for_column_name_collision(Relation rel, const char *colname,
bool if_not_exists);
static void add_column_datatype_dependency(Oid relid, int32 attnum, Oid typid);
static void add_column_collation_dependency(Oid relid, int32 attnum, Oid collid);
static void ATPrepAddOids(List **wqueue, Relation rel, bool recurse,
Expand Down Expand Up @@ -2304,7 +2305,7 @@ renameatt_internal(Oid myrelid,
oldattname)));

/* new name should not already exist */
check_for_column_name_collision(targetrelation, newattname);
(void) check_for_column_name_collision(targetrelation, newattname, false);

/* apply the update */
namestrcpy(&(attform->attname), newattname);
Expand Down Expand Up @@ -3455,11 +3456,11 @@ ATExecCmd(List **wqueue, AlteredTableInfo *tab, Relation rel,
case AT_AddColumnToView: /* add column via CREATE OR REPLACE
* VIEW */
address = ATExecAddColumn(wqueue, tab, rel, (ColumnDef *) cmd->def,
false, false, false, lockmode);
false, false, false, false, lockmode);
break;
case AT_AddColumnRecurse:
address = ATExecAddColumn(wqueue, tab, rel, (ColumnDef *) cmd->def,
false, true, false, lockmode);
false, true, false, cmd->missing_ok, lockmode);
break;
case AT_ColumnDefault: /* ALTER COLUMN DEFAULT */
address = ATExecColumnDefault(rel, cmd->name, cmd->def, lockmode);
Expand Down Expand Up @@ -3572,14 +3573,14 @@ ATExecCmd(List **wqueue, AlteredTableInfo *tab, Relation rel,
if (cmd->def != NULL)
address =
ATExecAddColumn(wqueue, tab, rel, (ColumnDef *) cmd->def,
true, false, false, lockmode);
true, false, false, cmd->missing_ok, lockmode);
break;
case AT_AddOidsRecurse: /* SET WITH OIDS */
/* Use the ADD COLUMN code, unless prep decided to do nothing */
if (cmd->def != NULL)
address =
ATExecAddColumn(wqueue, tab, rel, (ColumnDef *) cmd->def,
true, true, false, lockmode);
true, true, false, cmd->missing_ok, lockmode);
break;
case AT_DropOids: /* SET WITHOUT OIDS */

Expand Down Expand Up @@ -4677,7 +4678,7 @@ ATPrepAddColumn(List **wqueue, Relation rel, bool recurse, bool recursing,
static ObjectAddress
ATExecAddColumn(List **wqueue, AlteredTableInfo *tab, Relation rel,
ColumnDef *colDef, bool isOid,
bool recurse, bool recursing, LOCKMODE lockmode)
bool recurse, bool recursing, bool if_not_exists, LOCKMODE lockmode)
{
Oid myrelid = RelationGetRelid(rel);
Relation pgclass,
Expand Down Expand Up @@ -4771,8 +4772,14 @@ ATExecAddColumn(List **wqueue, AlteredTableInfo *tab, Relation rel,
elog(ERROR, "cache lookup failed for relation %u", myrelid);
relkind = ((Form_pg_class) GETSTRUCT(reltup))->relkind;

/* new name should not already exist */
check_for_column_name_collision(rel, colDef->colname);
/* skip if the name already exists and if_not_exists is true */
if (!check_for_column_name_collision(rel, colDef->colname, if_not_exists))
{
heap_close(attrdesc, RowExclusiveLock);
heap_freetuple(reltup);
heap_close(pgclass, RowExclusiveLock);
return InvalidObjectAddress;
}

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

/* Recurse to child; return value is ignored */
ATExecAddColumn(wqueue, childtab, childrel,
colDef, isOid, recurse, true, lockmode);
colDef, isOid, recurse, true,
if_not_exists, lockmode);

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

/*
* If a new or renamed column will collide with the name of an existing
* column, error out.
* column and if_not_exists is false then error out, else do nothing.
*/
static void
check_for_column_name_collision(Relation rel, const char *colname)
static bool
check_for_column_name_collision(Relation rel, const char *colname,
bool if_not_exists)
{
HeapTuple attTuple;
int attnum;
Expand All @@ -5029,7 +5038,7 @@ check_for_column_name_collision(Relation rel, const char *colname)
ObjectIdGetDatum(RelationGetRelid(rel)),
PointerGetDatum(colname));
if (!HeapTupleIsValid(attTuple))
return;
return true;

attnum = ((Form_pg_attribute) GETSTRUCT(attTuple))->attnum;
ReleaseSysCache(attTuple);
Expand All @@ -5045,10 +5054,23 @@ check_for_column_name_collision(Relation rel, const char *colname)
errmsg("column name \"%s\" conflicts with a system column name",
colname)));
else
{
if (if_not_exists)
{
ereport(NOTICE,
(errcode(ERRCODE_DUPLICATE_COLUMN),
errmsg("column \"%s\" of relation \"%s\" already exists, skipping",
colname, RelationGetRelationName(rel))));
return false;
}

ereport(ERROR,
(errcode(ERRCODE_DUPLICATE_COLUMN),
errmsg("column \"%s\" of relation \"%s\" already exists",
colname, RelationGetRelationName(rel))));
}

return true;
}

/*
Expand Down
20 changes: 20 additions & 0 deletions src/backend/parser/gram.y
View file
Expand Up @@ -1942,6 +1942,16 @@ alter_table_cmd:
AlterTableCmd *n = makeNode(AlterTableCmd);
n->subtype = AT_AddColumn;
n->def = $2;
n->missing_ok = false;
$$ = (Node *)n;
}
/* ALTER TABLE <name> ADD IF NOT EXISTS <coldef> */
| ADD_P IF_P NOT EXISTS columnDef
{
AlterTableCmd *n = makeNode(AlterTableCmd);
n->subtype = AT_AddColumn;
n->def = $5;
n->missing_ok = true;
$$ = (Node *)n;
}
/* ALTER TABLE <name> ADD COLUMN <coldef> */
Expand All @@ -1950,6 +1960,16 @@ alter_table_cmd:
AlterTableCmd *n = makeNode(AlterTableCmd);
n->subtype = AT_AddColumn;
n->def = $3;
n->missing_ok = false;
$$ = (Node *)n;
}
/* ALTER TABLE <name> ADD COLUMN IF NOT EXISTS <coldef> */
| ADD_P COLUMN IF_P NOT EXISTS columnDef
{
AlterTableCmd *n = makeNode(AlterTableCmd);
n->subtype = AT_AddColumn;
n->def = $6;
n->missing_ok = true;
$$ = (Node *)n;
}
/* ALTER TABLE <name> ALTER [COLUMN] <colname> {SET DEFAULT <expr>|DROP DEFAULT} */
Expand Down
89 changes: 89 additions & 0 deletions src/test/regress/expected/alter_table.out
View file
Expand Up @@ -2605,3 +2605,92 @@ ALTER TABLE logged1 SET UNLOGGED; -- silently do nothing
DROP TABLE logged3;
DROP TABLE logged2;
DROP TABLE logged1;
-- test ADD COLUMN IF NOT EXISTS
CREATE TABLE test_add_column(c1 integer);
\d test_add_column
Table "public.test_add_column"
Column | Type | Modifiers
--------+---------+-----------
c1 | integer |

ALTER TABLE test_add_column
ADD COLUMN c2 integer;
\d test_add_column
Table "public.test_add_column"
Column | Type | Modifiers
--------+---------+-----------
c1 | integer |
c2 | integer |

ALTER TABLE test_add_column
ADD COLUMN c2 integer; -- fail because c2 already exists
ERROR: column "c2" of relation "test_add_column" already exists
\d test_add_column
Table "public.test_add_column"
Column | Type | Modifiers
--------+---------+-----------
c1 | integer |
c2 | integer |

ALTER TABLE test_add_column
ADD COLUMN IF NOT EXISTS c2 integer; -- skipping because c2 already exists
NOTICE: column "c2" of relation "test_add_column" already exists, skipping
\d test_add_column
Table "public.test_add_column"
Column | Type | Modifiers
--------+---------+-----------
c1 | integer |
c2 | integer |

ALTER TABLE test_add_column
ADD COLUMN c2 integer, -- fail because c2 already exists
ADD COLUMN c3 integer;
ERROR: column "c2" of relation "test_add_column" already exists
\d test_add_column
Table "public.test_add_column"
Column | Type | Modifiers
--------+---------+-----------
c1 | integer |
c2 | integer |

ALTER TABLE test_add_column
ADD COLUMN IF NOT EXISTS c2 integer, -- skipping because c2 already exists
ADD COLUMN c3 integer; -- fail because c3 already exists
NOTICE: column "c2" of relation "test_add_column" already exists, skipping
\d test_add_column
Table "public.test_add_column"
Column | Type | Modifiers
--------+---------+-----------
c1 | integer |
c2 | integer |
c3 | integer |

ALTER TABLE test_add_column
ADD COLUMN IF NOT EXISTS c2 integer, -- skipping because c2 already exists
ADD COLUMN IF NOT EXISTS c3 integer; -- skipping because c3 already exists
NOTICE: column "c2" of relation "test_add_column" already exists, skipping
NOTICE: column "c3" of relation "test_add_column" already exists, skipping
\d test_add_column
Table "public.test_add_column"
Column | Type | Modifiers
--------+---------+-----------
c1 | integer |
c2 | integer |
c3 | integer |

ALTER TABLE test_add_column
ADD COLUMN IF NOT EXISTS c2 integer, -- skipping because c2 already exists
ADD COLUMN IF NOT EXISTS c3 integer, -- skipping because c3 already exists
ADD COLUMN c4 integer;
NOTICE: column "c2" of relation "test_add_column" already exists, skipping
NOTICE: column "c3" of relation "test_add_column" already exists, skipping
\d test_add_column
Table "public.test_add_column"
Column | Type | Modifiers
--------+---------+-----------
c1 | integer |
c2 | integer |
c3 | integer |
c4 | integer |

DROP TABLE test_add_column;
31 changes: 31 additions & 0 deletions src/test/regress/sql/alter_table.sql
View file
Expand Up @@ -1724,3 +1724,34 @@ ALTER TABLE logged1 SET UNLOGGED; -- silently do nothing
DROP TABLE logged3;
DROP TABLE logged2;
DROP TABLE logged1;

-- test ADD COLUMN IF NOT EXISTS
CREATE TABLE test_add_column(c1 integer);
\d test_add_column
ALTER TABLE test_add_column
ADD COLUMN c2 integer;
\d test_add_column
ALTER TABLE test_add_column
ADD COLUMN c2 integer; -- fail because c2 already exists
\d test_add_column
ALTER TABLE test_add_column
ADD COLUMN IF NOT EXISTS c2 integer; -- skipping because c2 already exists
\d test_add_column
ALTER TABLE test_add_column
ADD COLUMN c2 integer, -- fail because c2 already exists
ADD COLUMN c3 integer;
\d test_add_column
ALTER TABLE test_add_column
ADD COLUMN IF NOT EXISTS c2 integer, -- skipping because c2 already exists
ADD COLUMN c3 integer; -- fail because c3 already exists
\d test_add_column
ALTER TABLE test_add_column
ADD COLUMN IF NOT EXISTS c2 integer, -- skipping because c2 already exists
ADD COLUMN IF NOT EXISTS c3 integer; -- skipping because c3 already exists
\d test_add_column
ALTER TABLE test_add_column
ADD COLUMN IF NOT EXISTS c2 integer, -- skipping because c2 already exists
ADD COLUMN IF NOT EXISTS c3 integer, -- skipping because c3 already exists
ADD COLUMN c4 integer;
\d test_add_column
DROP TABLE test_add_column;

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