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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：
SQL代码：
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 collectDECLARE 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;sql代码
--UPDATE statement is sent to the SQL engine just once, with the entire nested tableFORALL 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.
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