| Oracle FAQ | Your Portal to the Oracle Knowledge Grid | |
 |
 | |||
| Oracle FAQ | Your Portal to the Oracle Knowledge Grid | |
|
| |||
Home -> Community -> Mailing Lists -> Oracle-L -> About Bulk Collect
Here is a very brief introduction to bulk collect if you never heard about
it.
There are to engines to run PL/SQL blocks and subprograms.
PL/SQL engine runs procedural statements, while the SQL engine runs SQL
statements.
During execution, every SQL statement causes a context switch between the
two engines. Performance can be improved reducing the number of contexts
switches using FORALL for bulk collection.
Without the bulk bind, PL/SQL sends a SQL statement to the SQL engine for
each DML( Insert, Update, Delete) command you can use too with SELECT
statements.
DECLARE
TYPE Numlist IS VARRAY (100) OF NUMBER;
Id NUMLIST := NUMLIST(7902, 7698, 7839);
BEGIN
-- Efficient method, using a bulk bind
FORALL i IN Id.FIRST..Id.LAST -- bulk-bind the VARRAY
UPDATE Emp_tab SET Sal = 1.1 * Sal
WHERE Mgr = Id(i);
-- Slower method, running the UPDATE statements within a regular loop
FOR i IN Id.FIRST..Id.LAST LOOP
UPDATE Emp_tab SET Sal = 1.1 * Sal
WHERE Mgr = Id(i);
END LOOP;
END;
DECLARE
TYPE Var_tab IS TABLE OF VARCHAR2(20) INDEX BY BINARY_INTEGER;
Empno VAR_TAB;
Ename VAR_TAB;
Counter NUMBER;
CURSOR C IS SELECT Empno, Ename FROM Emp_tab WHERE Mgr = 7698;
BEGIN
-- Efficient method, using a bulk bind
SELECT Empno, Ename BULK COLLECT INTO Empno, Ename
FROM Emp_Tab WHERE Mgr = 7698;
-- Slower method, assigning each collection element within a loop.
counter := 1;
FOR rec IN C LOOP
Empno(Counter) := rec.Empno;
Ename(Counter) := rec.Ename;
Counter := Counter + 1;
END LOOP;
END;
DECLARE
TYPE NumList IS VARRAY(20) OF NUMBER;
depts NumList := NumList(10, 30, 70); -- department numbers
BEGIN
FORALL i IN depts.FIRST..depts.LAST
DELETE FROM emp WHERE deptno = depts(i);
END;
DECLARE
TYPE NumTab IS TABLE OF NUMBER(4) INDEX BY BINARY_INTEGER;
TYPE NameTab IS TABLE OF CHAR(15) INDEX BY BINARY_INTEGER;
pnums NumTab;
pnames NameTab;
BEGIN
FOR j IN 1..5000 LOOP -- load index-by tables
pnums(j) := j;
pnames(j) := 'Part No. ' || TO_CHAR(j);
END LOOP;
FORALL i IN 1..5000 -- use FORALL statement
INSERT INTO parts VALUES (pnums(i), pnames(i));
FOR i IN 1..5000 LOOP -- use FOR loop
INSERT INTO parts VALUES (pnums(i), pnames(i));
END LOOP;
END;
To use bulk operation read PL/SQL users guides and reference, to know about
more features of bulk operations.
 |
 |