3.2 Adding Value

Chapter 3
The PL/SQL Development Spiral

 

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Sometimes it is worth stepping back and searching for the bigger picture before embarking on one's enhancements. In this case, I find myself wondering what other twists and turns I might encounter in my application development. Since I need UPPER-lower string duplication, I might also run into a requirement to perform lower-UPPER string duplication. As long as I am changing the twice function for one of these variations, I should try to stay ahead of the game and handle both variations.

So I will restate the new requirements of twice: double the specified string. Return the new string with the same case as the original, and return it in UPPER-lower or return it in lower-UPPER, depending on the user request.

When stated in this way, an obvious question pops up: how is the user going to specify the case handling in the call to twice? For a standalone function, this means adding a parameter. Instead of just accepting the string value for doubling, twice must also receive the type of action to perform. The new header for twice, therefore, must be:

FUNCTION twice (string_in IN VARCHAR2, action_in IN VARCHAR2)

where the action can be one of these values:

N

No change to case

UL

UPPER-lower case conversion

LU

lower-UPPER case conversion

Once the parameter and valid options are in place, the implementation is straightforward (and is shown in Example 3.2). I simply use an IF statement to direct the runtime engine to the right RETURN statement.

Example 3.2: The twice Function with Alternative Actions

CREATE OR REPLACE FUNCTION twice     (string_in IN VARCHAR2, action_in IN VARCHAR2) RETURN VARCHAR2 IS BEGIN    IF action_in = 'UL'    THEN       RETURN (UPPER (string_in) || LOWER (string_in));                 ELSIF action_in = 'LU'    THEN       RETURN (LOWER (string_in) || UPPER (string_in));                 ELSIF action_in = 'N'     THEN       RETURN string_in || string_in;    END IF;  END twice;