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Oracle 之 bulk collect 的用法

2009-10-11 12:21 302 查看

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

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

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