Append oracle associative array in a loop to another associative array within that loop - sql

Question

I am trying to do to a bulk collect inside a loop which have dynamic SQL and execute multiple times based on input from loop then inserting into a table (and it is taking time approx. 4 mins to insert 193234 records).
So as to try different different approach I think of using the bulk collect on select inside the loop and fill up a collection with each iteration of that loop lets say 1st iteration gives 10 rows then second gives 0 rows and 3rd returns 15 rows then the collection should hold 15 records at end of the loop.
After exiting the loop I will use forall with collection I filled up inside loop to do an Insert at one go instead to doing insert for each iteration inside loop.
below is a sample code which is similar to application procedure I just use different tables to simplify question.
create table test_tab as select owner, table_name, column_name from all_tab_cols where 1=2;
create or replace procedure p_test
as
l_sql varchar2(4000);
type t_tab is table of test_tab%rowtype index by pls_integer;
l_tab t_tab;
l_tab1 t_tab;
l_cnt number := 0;
begin
for i in (with tab as (select 'V_$SESSION' table_name from dual
union all
select 'any_table' from dual
union all
select 'V_$TRANSACTION' from dual
union all
select 'test_table' from dual
)
select table_name from tab )
loop
l_sql := 'select owner, table_name, column_name from all_tab_cols where table_name = '''||i.table_name||'''';
-- dbms_output.put_line(l_sql );
execute immediate l_sql bulk collect into l_tab;
dbms_output.put_line(l_sql ||' > '||l_tab.count);
l_cnt := l_cnt +1;
if l_tab.count<>0
then
l_tab1(l_cnt) := l_tab(l_cnt);
end if;
end loop;
dbms_output.put_line(l_tab1.count);
forall i in indices of l_tab1
insert into test_tab values (l_tab1(i).owner, l_tab1(i).table_name, l_tab1(i).column_name);
end;
It is inserting only 2 rows in test_tab table whereas as per my system it should insert 150 rows.
select owner, table_name, column_name from all_tab_cols where table_name = 'V_$SESSION' > 103
select owner, table_name, column_name from all_tab_cols where table_name = 'any_table' > 0
select owner, table_name, column_name from all_tab_cols where table_name = 'V_$TRANSACTION' > 47
select owner, table_name, column_name from all_tab_cols where table_name = 'test_table' > 0
2
Above is DBMS_OUTPUT from my system you may change the table names in loop if the example table names does not exists in your DB.
Oracle Version --
Oracle Database 19c Standard Edition 2 Release 19.0.0.0.0 - Production
EDIT
Below screenshot shows highlighted timings from PLSQL_PROFILER with Actual insert...select... written in procedure at line# 114 and with bulk collect and forall with nested table at line# 132 and multiset and seems like we are saving atleast 40 secs here with bulk collect, multiset and forall.

Answer 1

Firstly, do not use associative array collection for this, just use a nested-table collection type. You can concatenate nested-table collections using the MULTISET UNION ALL operator (avoiding needing to use loops).
CREATE TYPE test_type IS OBJECT(
owner VARCHAR2(30),
table_name VARCHAR2(30),
column_name VARCHAR2(30)
);
CREATE TYPE test_tab_type IS TABLE OF test_type;
Then:
create procedure p_test
as
l_sql CLOB := 'select test_type(owner, table_name, column_name) from all_tab_cols where table_name = :table_name';
l_table_names SYS.ODCIVARCHAR2LIST := SYS.ODCIVARCHAR2LIST(
'V_$SESSION',
'ANY_TABLE',
'V_$TRANSACTION',
'TEST_TABLE'
);
l_tab test_tab_type := test_tab_type();
l_temp test_tab_type;
l_cnt number := 0;
BEGIN
FOR i IN 1 .. l_table_names.COUNT LOOP
EXECUTE IMMEDIATE l_sql BULK COLLECT INTO l_temp USING l_table_names(i);
dbms_output.put_line(
l_sql || ': ' || l_table_names(i) || ' > '||l_temp.count
);
l_cnt := l_cnt +1;
l_tab := l_tab MULTISET UNION ALL l_temp;
END LOOP;
dbms_output.put_line(l_tab.count);
insert into test_tab
SELECT *
FROM TABLE(l_tab);
end;
/
Secondly, don't do multiple queries if you can do it all in one query and use an IN statement; and if you do it all in a single statement then you do not need to worry about concatenating collections.
create or replace procedure p_test
as
l_table_names SYS.ODCIVARCHAR2LIST := SYS.ODCIVARCHAR2LIST(
'V_$SESSION',
'ANY_TABLE',
'V_$TRANSACTION',
'TEST_TABLE'
);
l_tab test_tab_type;
BEGIN
select test_type(owner, table_name, column_name)
bulk collect into l_tab
from all_tab_cols
where table_name IN (SELECT column_value FROM TABLE(l_table_names));
dbms_output.put_line(l_tab.count);
insert into test_tab
SELECT *
FROM TABLE(l_tab);
end;
/
Thirdly, if you can do INSERT ... SELECT ... in a single statement the it will be much faster than using SELECT ... INTO ... and then a separate INSERT; and doing that means you do not need to use any collections.
create or replace procedure p_test
as
begin
INSERT INTO test_tab (owner, table_name, column_name)
select owner, table_name, column_name
from all_tab_cols
where table_name IN (
'V_$SESSION',
'ANY_TABLE',
'V_$TRANSACTION',
'TEST_TABLE'
);
end;
/
fiddle

Answer 2

For Oracle 19c I would suggest to use SQL_MACRO(table) to build dynamic SQL in place and use plain SQL. Below is an example that builds dynamic SQL based on all_tab_cols but it may be any other logic to build such SQL (with known column names and column order). Then you may use insert ... select ... without PL/SQL, because SQL macro is processed at the query parsing time.
Setup:
create table t1
as
select level as id, mod(level, 2) as val, mod(level, 2) as col
from dual
connect by level < 4;
create table t2
as
select level as id2, mod(level, 2) as val2, mod(level, 2) as col2
from dual
connect by level < 5;
create table t3
as
select level as id3, mod(level, 2) as val3, mod(level, 2) as col3
from dual
connect by level < 6;
Usage:
create function f_union_tables
return varchar2 sql_macro(table)
as
l_sql varchar2(4000);
begin
/*
Below query emulates dynamic SQL with union
of counts per columns COL* and VAL* per table,
assuming you have only one such column in a table
*/
select
listagg(
replace(replace(
/*Get a count per the second and the third column per table*/
q'{
select '$$table_name$$' as table_name, $$agg_cols$$, count(*) as cnt
from $$table_name$$
group by $$agg_cols$$
}',
'$$table_name$$', table_name),
'$$agg_cols$$', listagg(column_name, ' ,') within group(order by column_name asc)
),
chr(10) || ' union all ' || chr(10)
) within group (order by table_name) as result_sql
into l_sql
from user_tab_cols
where regexp_like(table_name, '^T\d+$')
and (
column_name like 'VAL%'
or column_name like 'COL%'
)
group by table_name;
return l_sql;
end;/
select *
from f_union_tables()
TABLE_NAME
COL
VAL
CNT
T1
1
1
2
T1
0
0
1
T2
1
1
2
T2
0
0
2
T3
1
1
3
T3
0
0
2
fiddle