浅谈Oracle性能优化可能出现的问题

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浅谈Oracle性能优化可能出现的问题

发表于：2010-5-26 10:47

作者：未知来源：51Testing软件测试网采编

　　用exit跳出循环，通常情况下，exit只跳出当前层的循环，与其它程序设计语言的break语句类似。在嵌套的循环中，如果要直接从内层循环跳出外面多层的循环，可使用'EXIT 标签 When'形式的语句，举例如下：

1    SQL>   BEGIN
2          <>
3          FOR v_outerloopcounter IN 1..2 LOOP
4               <>
5               FOR v_innerloopcounter IN 1..4 LOOP
6                    DBMS_OUTPUT.PUT_LINE('Outer Loop counter is '
7                         || v_outerloopcounter ||
8                         ' Inner Loop counter is ' || v_innerloopcounter);
9                         EXIT WHEN v_innerloopcounter = 3;
10              END LOOP innerloop;
11         END LOOP outerloop;
12    END;
13    /
Outer Loop counter is 1 Inner Loop counter is 1
Outer Loop counter is 1 Inner Loop counter is 2
Outer Loop counter is 1 Inner Loop counter is 3
Outer Loop counter is 2 Inner Loop counter is 1
Outer Loop counter is 2 Inner Loop counter is 2
Outer Loop counter is 2 Inner Loop counter is 3
PL/SQL procedure successfully completed.

　　从上面可以看出，普通情况下，exit只跳出当前层的循环。

1    SQL>   BEGIN
2          <>
3          FOR v_outerloopcounter IN 1..2 LOOP
4               <>
5               FOR v_innerloopcounter IN 1..4 LOOP
6                    DBMS_OUTPUT.PUT_LINE('Outer Loop counter is '
7                         || v_outerloopcounter ||
8                         ' Inner Loop counter is ' || v_innerloopcounter);
9                         EXIT outerloop WHEN v_innerloopcounter = 3;
10              END LOOP innerloop;
11         END LOOP outerloop;
12    END;
13    /
Outer Loop counter is 1 Inner Loop counter is 1
Outer Loop counter is 1 Inner Loop counter is 2
Outer Loop counter is 1 Inner Loop counter is 3
PL/SQL procedure successfully completed.

　　从上面可以看出，exit跳出了外层的循环。

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