oracle pl/sql（bulk collect用法）

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;