Implement OR REPLACE option for CREATE AGGREGATE.

Aggregates have acquired a dozen or so optional attributes in recent
years for things like parallel query and moving-aggregate mode; the
lack of an OR REPLACE option to add or change these for an existing
agg makes extension upgrades gratuitously hard. Rectify.

2 files changed, 136 insertions, 0 deletions

diff --git a/src/test/regress/expected/create_aggregate.out b/src/test/regress/expected/create_aggregate.out
index 3d92084e130..a2eb9996e15 100644
--- a/src/test/regress/expected/create_aggregate.out
+++ b/src/test/regress/expected/create_aggregate.out
@@ -161,6 +161,77 @@ WHERE aggfnoid = 'myavg'::REGPROC;
 (1 row)
 
 DROP AGGREGATE myavg (numeric);
+-- create or replace aggregate
+CREATE AGGREGATE myavg (numeric)
+(
+	stype = internal,
+	sfunc = numeric_avg_accum,
+	finalfunc = numeric_avg
+);
+CREATE OR REPLACE AGGREGATE myavg (numeric)
+(
+	stype = internal,
+	sfunc = numeric_avg_accum,
+	finalfunc = numeric_avg,
+	serialfunc = numeric_avg_serialize,
+	deserialfunc = numeric_avg_deserialize,
+	combinefunc = numeric_avg_combine,
+	finalfunc_modify = shareable  -- just to test a non-default setting
+);
+-- Ensure all these functions made it into the catalog again
+SELECT aggfnoid, aggtransfn, aggcombinefn, aggtranstype::regtype,
+       aggserialfn, aggdeserialfn, aggfinalmodify
+FROM pg_aggregate
+WHERE aggfnoid = 'myavg'::REGPROC;
+ aggfnoid |    aggtransfn     |    aggcombinefn     | aggtranstype |      aggserialfn      |      aggdeserialfn      | aggfinalmodify 
+----------+-------------------+---------------------+--------------+-----------------------+-------------------------+----------------
+ myavg    | numeric_avg_accum | numeric_avg_combine | internal     | numeric_avg_serialize | numeric_avg_deserialize | s
+(1 row)
+
+-- can change stype:
+CREATE OR REPLACE AGGREGATE myavg (numeric)
+(
+	stype = numeric,
+	sfunc = numeric_add
+);
+SELECT aggfnoid, aggtransfn, aggcombinefn, aggtranstype::regtype,
+       aggserialfn, aggdeserialfn, aggfinalmodify
+FROM pg_aggregate
+WHERE aggfnoid = 'myavg'::REGPROC;
+ aggfnoid | aggtransfn  | aggcombinefn | aggtranstype | aggserialfn | aggdeserialfn | aggfinalmodify 
+----------+-------------+--------------+--------------+-------------+---------------+----------------
+ myavg    | numeric_add | -            | numeric      | -           | -             | r
+(1 row)
+
+-- can't change return type:
+CREATE OR REPLACE AGGREGATE myavg (numeric)
+(
+	stype = numeric,
+	sfunc = numeric_add,
+	finalfunc = numeric_out
+);
+ERROR:  cannot change return type of existing function
+HINT:  Use DROP AGGREGATE myavg(numeric) first.
+-- can't change to a different kind:
+CREATE OR REPLACE AGGREGATE myavg (order by numeric)
+(
+	stype = numeric,
+	sfunc = numeric_add
+);
+ERROR:  cannot change routine kind
+DETAIL:  "myavg" is an ordinary aggregate function.
+-- can't change plain function to aggregate:
+create function sum4(int8,int8,int8,int8) returns int8 as
+'select $1 + $2 + $3 + $4' language sql strict immutable;
+CREATE OR REPLACE AGGREGATE sum3 (int8,int8,int8)
+(
+	stype = int8,
+	sfunc = sum4
+);
+ERROR:  cannot change routine kind
+DETAIL:  "sum3" is a function.
+drop function sum4(int8,int8,int8,int8);
+DROP AGGREGATE myavg (numeric);
 -- invalid: bad parallel-safety marking
 CREATE AGGREGATE mysum (int)
 (
diff --git a/src/test/regress/sql/create_aggregate.sql b/src/test/regress/sql/create_aggregate.sql
index cb6552e2d68..fd7cd400c19 100644
--- a/src/test/regress/sql/create_aggregate.sql
+++ b/src/test/regress/sql/create_aggregate.sql
@@ -174,6 +174,71 @@ WHERE aggfnoid = 'myavg'::REGPROC;
 
 DROP AGGREGATE myavg (numeric);
 
+-- create or replace aggregate
+CREATE AGGREGATE myavg (numeric)
+(
+	stype = internal,
+	sfunc = numeric_avg_accum,
+	finalfunc = numeric_avg
+);
+
+CREATE OR REPLACE AGGREGATE myavg (numeric)
+(
+	stype = internal,
+	sfunc = numeric_avg_accum,
+	finalfunc = numeric_avg,
+	serialfunc = numeric_avg_serialize,
+	deserialfunc = numeric_avg_deserialize,
+	combinefunc = numeric_avg_combine,
+	finalfunc_modify = shareable  -- just to test a non-default setting
+);
+
+-- Ensure all these functions made it into the catalog again
+SELECT aggfnoid, aggtransfn, aggcombinefn, aggtranstype::regtype,
+       aggserialfn, aggdeserialfn, aggfinalmodify
+FROM pg_aggregate
+WHERE aggfnoid = 'myavg'::REGPROC;
+
+-- can change stype:
+CREATE OR REPLACE AGGREGATE myavg (numeric)
+(
+	stype = numeric,
+	sfunc = numeric_add
+);
+SELECT aggfnoid, aggtransfn, aggcombinefn, aggtranstype::regtype,
+       aggserialfn, aggdeserialfn, aggfinalmodify
+FROM pg_aggregate
+WHERE aggfnoid = 'myavg'::REGPROC;
+
+-- can't change return type:
+CREATE OR REPLACE AGGREGATE myavg (numeric)
+(
+	stype = numeric,
+	sfunc = numeric_add,
+	finalfunc = numeric_out
+);
+
+-- can't change to a different kind:
+CREATE OR REPLACE AGGREGATE myavg (order by numeric)
+(
+	stype = numeric,
+	sfunc = numeric_add
+);
+
+-- can't change plain function to aggregate:
+create function sum4(int8,int8,int8,int8) returns int8 as
+'select $1 + $2 + $3 + $4' language sql strict immutable;
+
+CREATE OR REPLACE AGGREGATE sum3 (int8,int8,int8)
+(
+	stype = int8,
+	sfunc = sum4
+);
+
+drop function sum4(int8,int8,int8,int8);
+
+DROP AGGREGATE myavg (numeric);
+
 -- invalid: bad parallel-safety marking
 CREATE AGGREGATE mysum (int)
 (