UNION operator with BULK COLLECT for a collection type

Question

Hi all,
I created a table type as below:
create or replace type coltest is table of number;
Below are 3 PL/SQL blocks that populate data into variables of the above mentioned table type:
BLOCK 1:
DECLARE
col1 coltest := coltest(1, 2, 3, 4, 5, 11);
col2 coltest := coltest(6, 7, 8, 9, 10);
col3 coltest := coltest();
BEGIN
SELECT * BULK COLLECT
INTO col1
FROM (SELECT *
FROM TABLE(CAST(col1 AS coltest))
UNION ALL
SELECT * FROM TABLE(CAST(col2 AS coltest)));
dbms_output.put_line('col1');
dbms_output.put_line('col1.count: ' || col1.COUNT);
FOR i IN 1 .. col1.COUNT
LOOP
dbms_output.put_line(col1(i));
END LOOP;
END;
OUPUT:
col1
col1.count: 5
6
7
8
9
10
BLOCK 2:
DECLARE
col1 coltest := coltest(1, 2, 3, 4, 5, 11);
col2 coltest := coltest(6, 7, 8, 9, 10);
col3 coltest := coltest();
BEGIN
SELECT * BULK COLLECT
INTO col2
FROM (SELECT *
FROM TABLE(CAST(col1 AS coltest))
UNION ALL
SELECT * FROM TABLE(CAST(col2 AS coltest)));
dbms_output.put_line('col2');
dbms_output.put_line('col2.count: ' || col2.COUNT);
FOR i IN 1 .. col2.COUNT
LOOP
dbms_output.put_line(col2(i));
END LOOP;
END;
OUTPUT:
col2
col2.count: 6
1
2
3
4
5
11
BLOCK 3:
DECLARE
col1 coltest := coltest(1, 2, 3, 4, 5, 11);
col2 coltest := coltest(6, 7, 8, 9, 10);
col3 coltest := coltest();
BEGIN
SELECT * BULK COLLECT
INTO col3
FROM (SELECT *
FROM TABLE(CAST(col1 AS coltest))
UNION ALL
SELECT * FROM TABLE(CAST(col2 AS coltest)));
dbms_output.put_line('col3');
dbms_output.put_line('col3.count: ' || col3.COUNT);
FOR i IN 1 .. col3.COUNT
LOOP
dbms_output.put_line(col3(i));
END LOOP;
END;
OUTPUT:
col3
col3.count: 11
1
2
3
4
5
11
6
7
8
9
10
Can anyone please explain the output of BLOCK 1 and 2? Why doesn't bulk collect into col1 and col2 return 11 as count?

Answer 1

Consider the following code from your block.
select *
  bulk collect into col1
  from (
         select *
           from table(cast(col1 as coltest))
          union
            all
         select *
           from table(cast(col2 as coltest))
       ); Now my assumption would be like this.
PL/SQL engine would recognize the SQL part and will be sending it to SQL Engine for processing. Before doing that it will try to initialize the SQL collection variable COL1. Now when SQL Engine process the SELECT, COL1 would be empty already. And thats the reason you don't get the as 5 and not 11.