TIPTOP 优化思想bulk collect 学习

通过bulk collect减少loop处理的开销 

采用bulk collect可以将查询结果一次性地加载到collections中。 
而不是通过cursor一条一条地处理。 
可以在select into,fetch into,returning into语句使用bulk collect。 
注意在使用bulk collect时，所有的into变量都必须是collections. 


举几个简单的例子： 
--在select into语句中使用bulk collect 
DECLARE 
TYPE SalList IS TABLE OF emp.sal%TYPE; 
sals SalList; 
BEGIN 
-- Limit the number of rows to 100. 
SELECT sal BULK COLLECT INTO sals FROM emp 
WHERE ROWNUM <= 100; 
-- Retrieve 10% (approximately) of the rows in the table. 
SELECT sal BULK COLLECT INTO sals FROM emp SAMPLE 10; 
END; 
/ 
--在fetch into中使用bulk collect 
DECLARE 
TYPE DeptRecTab IS TABLE OF dept%ROWTYPE; 
dept_recs DeptRecTab; 
CURSOR c1 IS 
SELECT deptno, dname, loc FROM dept WHERE deptno > 10; 
BEGIN 
OPEN c1; 
FETCH c1 BULK COLLECT INTO dept_recs; 
END; 
/ 
--在returning into中使用bulk collect 
CREATE TABLE emp2 AS SELECT * FROM employees; 
DECLARE 
TYPE NumList IS TABLE OF employees.employee_id%TYPE; 
enums NumList; 
TYPE NameList IS TABLE OF employees.last_name%TYPE; 
names NameList; 
BEGIN 
DELETE FROM emp2 WHERE department_id = 30 
RETURNING employee_id, last_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('Employee #' || enums(i) || ': ' || names(i)); 
END LOOP; 
END; 
/ 
DROP TABLE emp2;