flush status;
show  status like "%custom_aggregate%";
Variable_name	Value
Feature_custom_aggregate_functions	0
create table t2 (sal int(10));
create table t3 (sal int(10),id int);
insert into t3 values (0,1),(1,2),(2,3),(3,4);
create aggregate function f1(x INT) returns int
begin
declare tot_sum int default 0;
declare continue handler for not found return tot_sum;
loop
fetch group next row;
set tot_sum= tot_sum + x;
end loop;
end|
create aggregate function f2 (x int) returns int
begin
declare counter int default 0;
declare continue handler for not found return 0;
loop
fetch group next row;
set counter =counter + (select f1(sal) from t1); 
end loop;
end|
create table t1 (sal int(10),id int(10));
INSERT INTO t1 (sal,id) VALUES (5000,1);
INSERT INTO t1 (sal,id) VALUES (2000,2);
INSERT INTO t1 (sal,id) VALUES (1000,3);
Normal select with custom aggregate function
select f1(sal) from t1 where id>= 1;
f1(sal)
8000
show  status like "%custom_aggregate%";
Variable_name	Value
Feature_custom_aggregate_functions	1
subqueries with custom aggregates
explain
select * from t1, (select f1(sal) as a  from t1 where id>= 1) q where q.a=t1.sal;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
1	PRIMARY	<derived2>	ref	key0	key0	5	test.t1.sal	2	
2	DERIVED	t1	ALL	NULL	NULL	NULL	NULL	3	Using where
show  status like "%custom_aggregate%";
Variable_name	Value
Feature_custom_aggregate_functions	2
explain
select * from t1, (select sal as a from t1 where (select f1(t3.sal) from t3) >=-1 ) q where q.a=t1.sal;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	
1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	Using where; Using join buffer (flat, BNL join)
3	SUBQUERY	t3	ALL	NULL	NULL	NULL	NULL	4	
show  status like "%custom_aggregate%";
Variable_name	Value
Feature_custom_aggregate_functions	3
explain
select (select f1(sal) as a from t3 where t3.id= t1.id )  from t1 ;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	
2	DEPENDENT SUBQUERY	t3	ALL	NULL	NULL	NULL	NULL	4	Using where
show  status like "%custom_aggregate%";
Variable_name	Value
Feature_custom_aggregate_functions	4
explain
select (select f1(sal) as a from t3 where t3.id= t1.id )  from t1 ;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	PRIMARY	t1	ALL	NULL	NULL	NULL	NULL	3	
2	DEPENDENT SUBQUERY	t3	ALL	NULL	NULL	NULL	NULL	4	Using where
show  status like "%custom_aggregate%";
Variable_name	Value
Feature_custom_aggregate_functions	5
custom aggregates inside other customm aggregates
explain
select f2(sal) from t1;
id	select_type	table	type	possible_keys	key	key_len	ref	rows	Extra
1	SIMPLE	t1	ALL	NULL	NULL	NULL	NULL	3	
show  status like "%custom_aggregate%";
Variable_name	Value
Feature_custom_aggregate_functions	6
cte with custom aggregates
with agg_sum as (
select f1(sal) from t1 where t1.id >=1 group by t1.id
)
select * from agg_sum;
f1(sal)
5000
2000
1000
show  status like "%custom_aggregate%";
Variable_name	Value
Feature_custom_aggregate_functions	7
drop table t2,t1,t3;
drop function f1;
drop function f2;