Two DML operations in one FORALL?

Question

Hi all,
In 11g is it possible to make two dml operations in one Forall loop?
For example:
SQL> create table xx_test (col1 number, col2 number, col3 number);
Table created
SQL> create table xx_test1 (col1 number, col2 number, col3 number);
Table created
SQL> insert into xx_test values(1,2,3);
1 row inserted
SQL>  insert into xx_test values(1,2,3);
1 row inserted
SQL>  insert into xx_test values(4,5,6);
1 row inserted
SQL>  insert into xx_test1 values(6,7,8);
1 row inserted
SQL> declare
  2  cursor c is select col1, col2, col3 from xx_test;
  3  type t is table of c%rowtype;
  4  v t;
  5  begin
  6   open c;
  7  loop
  8  fetch c bulk collect into v limit 1000;
  9   forall i in 1..v.count
10   update xx_test1
11  set col1 = v(i).col2;
12 
13  insert into xx_test1(col1,col2,col3) values(v(i).col1,v(i).col2,v(i).col3);
14 
15  exit when c%notfound;
16  end loop;
17 
18  end;
ORA-06550: line 14, column 50:
PLS-00201: identifier 'I' must be declared
ORA-06550: line 14, column 50:
PLS-00201: identifier 'I' must be declared
ORA-06550: line 14, column 48:
PL/SQL: ORA-00904: : invalid identifier
ORA-06550: line 14, column 4:
PL/SQL: SQL Statement ignoredany ideas? I know that this can be achieved by processing row by row but in my case the cursor retrieves a lot of rows...
Thanks in advance,
Alexander.

Answer 1

Stew, a bulk bind from an OCI client looks as follows:
OCIStmtPrepare()
OCIBindByName()/OCIBindByPos() (binding a host array)
while some-condition loop
  fill host array
  OCIStmtExecute()  (specify the number of elements in array via the iters param)
end loopThe statement is executed once for each array element - according to the OCI guide. So in the case of sending a 100 elements, the statement will be executed (iterated) by Oracle, a 100 times. It however is not exactly clear on how the server-side deals with this execution.
The issue you raised with cursor execution counts, seems to be whether the statement is single statement, or single statement with nested statements.
I have written an OCI client doing the exact same tests as were done in PL/SQL using FORALL in this thread.
If the SQL statement executed is SQL, the cursor that is created is executed only "once" (not exactly true as multiple rows are inserted using a single row DML).
If the statement is PL/SQL, the cursor that is created, is executed "once". So pretty much the same behaviour. However, as this statement contains "nested" SQLs (the actual DML statements), these also need to be parsed and executed as cursors. In which case you see these as being executed a 100 times (once per element in for the bind array).
The issue is whether or not the FORALL DML statement is executed once (as it would appear from the executions column), or not?
It would seem that there is some funky happening (some kind of call optimisation perhaps?) when Oracle deals with an array bind - as the cursor seems to be executed once. But that in fact is not the case as that cursor only inserts a single row. And multiple rows are inserted.
E.g. simplistic example to see how many times the FORALL DML statement is executed:
SQL> create sequence emp_id_seq
  2          start with 1
  3          increment by 1
  4          nocycle
  5          nomaxvalue;
Sequence created.
SQL> --// add a PL/SQL user function wrapper for the sequence
SQL> create or replace function GetNextEmpID return number is
  2          id      number;
  3  begin
  4          select emp_id_seq.NextVal into id from dual;  --// explicit SQL statement
  5          return( id );
  6  end;
  7  /
Function created.
SQL>
SQL> declare
  2          cursor c is
  3          select empno, ename, job from emp;
  4 
  5          type TBuffer is table of c%RowType;
  6          buffer  TBuffer;
  7  begin
  8          open c;
  9          loop
10                  fetch c bulk collect into buffer limit 100;
11 
12                  forall i in 1..buffer.Count
13                          insert into tab1 values( GetNextEmpID(), buffer(i).ename );
14                  exit when c%NotFound;
15          end loop;
16          close c;
17  end;
18  /
PL/SQL procedure successfully completed.
SQL>
SQL> select
  2          executions,
  3          sql_text
  4  from       v$sql
  5  where      sql_text like 'INSERT INTO TAB1%'
  6  or sql_text like 'SELECT EMP_ID_SEQ%';
EXECUTIONS SQL_TEXT
        14 SELECT EMP_ID_SEQ.NEXTVAL FROM DUAL
         1 INSERT INTO TAB1 VALUES( GETNEXTEMPID(), :B1So the insert seems to have been executed once. However, the wrapper was called 14 times and its SQL statement was called 14 times. Once per bind array value.
So there do seem to be some kind of optimisation on the Oracle side - however, it does not mean that the FORALL statement is not using bulk/array binding. It is. And that is what the FORALL statement is designed to do.