当Oracle运行PL/SQL时会使用两套引擎，所有procedural code由PL/SQL engine 完成，所有SQL由SQL engine处理。
所以假如Oracle从一个collection中循环执行相同的DML操作，那么为了避免两套engine切换所消耗的系统资源，可以使用bulk binds来把所有的DML操作binding到一次操作中完成。这将极大提高PL/SQL的执行效率。
以下是简单的测试，用两种方式插入100000条数据，可以看到效率提高了7倍左右。
代码:--------------------------------------------------------------------------------
SQL CREATE TABLE test1(
2id NUMBER(10),
3descriptionVARCHAR2(50));
Table created
SQL ALTER TABLE test1 ADD (
2CONSTRAINT test1_pk PRIMARY KEY (id));
Table altered
SQL SET TIMING ON;
SQL DECLARE
2TYPE id_typeIS TABLE OF test1.id%TYPE;
3TYPE description_type IS TABLE OF test1.description%TYPE;
4
5t_id id_type:= id_type();
6t_descriptiondescription_type := description_type();
7BEGIN
8FOR i IN 1 .. 100000 LOOP
9t_id.extend;
10t_description.extend;
11
12t_id(t_id.last) := i;
13t_description(t_description.last) := 'Description: ' To_Char(i);
14END LOOP;
15
16FOR i IN t_id.first .. t_id.last LOOP
17INSERT INTO test1 (id, description)
18VALUES (t_id(i), t_description(i));
19END LOOP;
20
21COMMIT;
22END;
23/
PL/SQL procedure sUCcessfully completed
Executed in 141.233 seconds
SQL truncate table test1;
Table truncated
Executed in 0.631 seconds
SQL
SQL DECLARE
2TYPE id_typeIS TABLE OF test1.id%TYPE;
3TYPE description_type IS TABLE OF test1.description%TYPE;
4
5t_id id_type:= id_type();
6t_descriptiondescription_type := description_type();
7BEGIN
8FOR i IN 1 .. 100000 LOOP
9t_id.extend;
10t_description.extend;
11
12t_id(t_id.last) := i;
13t_description(t_description.last) := 'Description: ' To_Char(i);
14END LOOP;
15
16FORALL i IN t_id.first .. t_id.last
17INSERT INTO test1 (id, description)
18VALUES (t_id(i), t_description(i));
19
20COMMIT;
21END;
22/
PL/SQL procedure successfully completed
Executed in 27.52 seconds
SQL select count(*) from test1;
COUNT(*)
----------
100000
Executed in 0.04 seconds
SQL--------------------------------------------------------------------------------
下面我们使用上面那个例子中插入的100000条数据，来测试一下BULK COLLECT的威力。
代码:--------------------------------------------------------------------------------
SQL SET TIMING ON;
SQL
SQL DECLARE
2TYPE id_typeIS TABLE OF test1.id%TYPE;
3TYPE description_type IS TABLE OF test1.description%TYPE;
4
5t_id id_type:= id_type();
6t_descriptiondescription_type := description_type();
7
8CURSOR c_data IS
9SELECT *
10FROM test1;
11BEGIN
12FOR cur_rec IN c_data LOOP
13t_id.extend;
14t_description.extend;
15
16t_id(t_id.last) := cur_rec.id;
17t_description(t_description.last) := cur_rec.description;
18END LOOP;
19END;
20/
PL/SQL procedure successfully completed
Executed in 2.974 seconds
SQL
SQL DECLARE
2TYPE id_typeIS TABLE OF test1.id%TYPE;
3TYPE description_type IS TABLE OF test1.description%TYPE;
4
5t_id id_type;
6t_descriptiondescription_type;
7BEGIN
8SELECT id, description
9BULK COLLECT INTO t_id, t_description FROM test1;
10END;
11/
PL/SQL procedure successfully completed
Executed in 0.371 seconds
SQL--------------------------------------------------------------------------------
结论：当我们需要将大量的检索结果放入一个collection的时候，使用bulking将比直接使用cursor循环有效的多。