通过bulk collect 减少loop处理的开销

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bulkcollect。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 collectDECLARE
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 collectDECLARE
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 collectCREATE 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;

感谢——转自 http://blog.sina.com.cn/s/blog_525394060100f822.html