ORACLE批量绑定FORALL与BULK COLLECT

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FORALL与BULK COLLECT的使用方法:
1．使用FORALL比FOR效率高，因为前者只切换一次上下文，而后者将是在循环次数一样多个上下文间切换。
2．使用BLUK COLLECT一次取出一个数据集合，比用游标条取数据效率高，尤其是在网络不大好的情况下。但BLUK COLLECT需要大量内存。
例子:

create table test_forall ( user_id number(10), user_name varchar2(20));

select into 中使用bulk collect

DECLARE
TYPE table_forall IS TABLE OF test_forall%ROWTYPE;
v_table table_forall;
BEGIN
SELECT mub.user_id,mub.user_name
BULK COLLECT INTO v_table
FROM mag_user_basic mub
WHERE mub.user_id BETWEEN 10000 AND 10100;
FORALL idx IN 1..v_table.COUNT
INSERT INTO test_forall VALUES v_table(idx);
--VALUES(v_table(idx).user_id,v_table(idx).user_name);Error
--在PL/SQL中，BULK In-BIND与RECORD，%ROWTYPE是不能在一块使用的，
--也就是说，BULK In-BIND只能与简单类型的数组一块使用
COMMIT;
EXCEPTION
WHEN OTHERS THEN
ROLLBACK;
END;

fetch into 中使用bulk collect

DECLARE
TYPE table_forall IS TABLE OF test_forall%ROWTYPE;
v_table table_forall;   
CURSOR c1 IS
SELECT mub.user_id,mub.user_name
FROM mag_user_basic mub
WHERE mub.user_id BETWEEN 10000 AND 10100;
BEGIN
OPEN c1;
--在fetch into中使用bulk collect
FETCH c1 BULK COLLECT INTO v_table;
FORALL idx IN 1..v_table.COUNT
INSERT INTO test_forall VALUES v_table(idx);
COMMIT;
EXCEPTION
WHEN OTHERS THEN
ROLLBACK;
END;

在returning into中使用bulk collect

CREATE TABLE test_forall2 AS SELECT * FROM test_forall;
----在returning into中使用bulk collect
DECLARE
TYPE IdList IS TABLE OF test_forall.User_Id%TYPE;
enums IdList;
TYPE NameList IS TABLE OF test_forall.user_name%TYPE;
names NameList;
BEGIN
DELETE FROM test_forall2 WHERE user_id = 10100
RETURNING user_id, user_name BULK COLLECT INTO enums, names;
dbms_output.put_line('Deleted ' || SQL%ROWCOUNT || ' rows:');
FOR i IN enums.FIRST .. enums.LAST
LOOP
dbms_output.put_line('User #' || enums(i) || ': ' || names(i));
END LOOP;
COMMIT;
EXCEPTION
WHEN OTHERS THEN
ROLLBACK;
END;

批量更新中，将for改成forall

DECLARE
TYPE NumList IS VARRAY(20) OF NUMBER;                                                
depts NumList := NumList(10, 30, 70, ...);
-- department numbers                    
BEGIN        
...           
FOR i IN depts.FIRST..depts.LAST
LOOP
...
--UPDATE statement is sent to the SQL engine
-- with each iteration of the FOR loop!
UPDATE emp SET sal = sal * 1.10 WHERE deptno = depts(i);
END LOOP:
END;         


--UPDATE statement is sent to the SQL engine just once, with the entire nested table
FORALL i IN depts.FIRST..depts.LAST
UPDATE emp SET sal = sal * 1.10 WHERE deptno = depts(i);

To maximize performance, rewrite your programs as follows:
a. If an INSERT, UPDATE, or DELETE statement executes inside a loop and References collection elements, move it into a FORALL statement.
b. If a SELECT INTO, FETCH INTO, or RETURNING INTO clause references a
Collection, incorporate the BULK COLLECT clause.
c. If possible, use host arrays to pass collections back and forth between your Programs and the database server.
d. If the failure of a DML operation on a particular row is not a serious problem,Include the keywords SAVE EXCEPTIONS in the FORALL statement and report Or clean up the errors in a subsequent loop using the %BULK_EXCEPTIONS Attribute.