采用bulk collect 可以将查询结果一次性的加载到collections中，而不是通过CURSOR一条一条地处理，可以在select into,fetchinto,
采用bulk collect 可以将查询结果一次性的加载到collections中，，而不是通过CURSOR一条一条地处理，可以在select into,fetchinto,returning into语句中使用bulk collect.
注意在使用bulk collect时，所有的into变量都必须是collections.
----在 select into语句中使用bulk collect
DECLARE
TYPE SalList IS TABLE OF emp.sal%TYPE;
sals SalList;
BEGIn
SELECT sal BULK COLLECT INTO sals FROM emp WHERE ROWNUM<=100;
SELECT sal BULK COLLECT INTO sals FROM emp SAMPLE 10;
----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%ROWCOUTN||'rows;');
FOR i IN enms.FIRST..enums.LAST
LOOP
DBMS_OUTPUT.PUT_LINE('Employee #'||enums(i)||';'||names(i));
END LOOP;
END;
/
Oracle 批量绑定forall bulk collect
批量绑定(Bulk binds)可以通过减少在pl/sql 和sql引擎之间的上下文切换(context switches)提高了性能
量绑定(Bulk binds)包括:
(i)Input collections,use the FORALL statement，用来改善DML(INSERT,UPDATE和DELETE)操作的性能。
(ii)Output collections,use the BULK COLLECT clause,一般用来提高查询(SELECT)的性能
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