2

我有严格的优化问题。当程序/函数被多次调用时，我应该在我的 PACKAGE 中放置 CONSTANT 变量吗？

让我们看看这个：

CREATE OR REPLACE PACKAGE WB_TEST IS
  PROCEDURE TEST;
END WB_TEST;

CREATE OR REPLACE PACKAGE BODY WB_TEST IS
  FUNCTION PARSER(IN_PARAM IN VARCHAR2) RETURN VARCHAR2 IS
    LC_MSG   CONSTANT VARCHAR2(80) := 'Hello USERNAME! How are you today?';
    LC_PARAM CONSTANT VARCHAR2(10) := 'USERNAME';
  BEGIN
    RETURN REPLACE(LC_MSG, LC_PARAM, IN_PARAM);
  END PARSER;

  PROCEDURE TEST IS
  BEGIN
    FOR I IN 1 .. 1000 LOOP
      DBMS_OUTPUT.PUT_LINE(PARSER(TO_CHAR(I)));
    END LOOP;
  END TEST;
BEGIN
  DBMS_OUTPUT.ENABLE(1000000);
END WB_TEST;
/

或者更好地做这样的事情：

CREATE OR REPLACE PACKAGE WB_TEST IS
  PROCEDURE TEST;
END WB_TEST;

CREATE OR REPLACE PACKAGE BODY WB_TEST IS
  GC_MSG   CONSTANT VARCHAR2(80) := 'Hello USERNAME! How are you today?';
  GC_PARAM CONSTANT VARCHAR2(10) := 'USERNAME';

  FUNCTION PARSER(IN_PARAM IN VARCHAR2) RETURN VARCHAR2 IS
  BEGIN
    RETURN REPLACE(GC_MSG, GC_PARAM, IN_PARAM);
  END PARSER;

  PROCEDURE TEST IS
  BEGIN
    FOR I IN 1 .. 1000 LOOP
      DBMS_OUTPUT.PUT_LINE(PARSER(TO_CHAR(I)));
    END LOOP;
  END TEST;
BEGIN
  DBMS_OUTPUT.ENABLE(1000000);
END WB_TEST;
4

1 回答 1

3

It is extremely unlikely to matter from a performance standpoint. The code the PL/SQL compiler generates should be identical in both cases-- the constants will almost certainly get compiled inline where they are referenced.

The only reason to prefer one over the other would be code clarity and variable scoping. If the constants are really local to the PARSER function-- if they aren't likely to be useful to other methods in the package, they ought to be declared as part of the function. If, on the other hand, they are likely to be useful to other methods in the package, they ought to be declared as part of the package body. If they are likely to be useful to methods outside the package, they ought to be declared as part of the package specification.

于 2012-09-20T17:29:21.583 回答