How Can Default Values Improve PostgreSQL Function Design for Variable Input Parameters?

Functions with Variable Input Parameters

When creating stored procedures (functions) in PostgreSQL, there's a need to handle updates to tables based on input parameters. To accommodate variable input parameters, one approach is to introduce a mode parameter. This mode parameter controls which specific parameters to use in the update query.

However, an alternative approach is to use default values for function parameters.

Default Values

By defining default values for function parameters, you can simplify the function and improve code readability. Consider the following example:

CREATE OR REPLACE FUNCTION update_site(_name text, _city text DEFAULT NULL, _telephone int DEFAULT NULL)
RETURNS int
LANGUAGE plpgsql AS
$func$
BEGIN
   IF _city IS NULL AND _telephone IS NULL THEN
      RAISE WARNING 'At least one not-null input value required!';
      RETURN;  -- nothing to update
   END IF;

   UPDATE "Sites"
   SET    "City"      = COALESCE(_city, "City")
        , "Telephone" = COALESCE(_telephone, "Telephone")
   WHERE  "SiteName"  = _name;
END
$func$;

Advantages of Default Values:

• Simplifies function code: No need for complex CASE statements or conditional logic based on mode parameters.
• Avoids naming conflicts: Using underscores prefixes for input parameters prevents clashes with column names.
• Enhances readability: Clearer and more intuitive function logic.

Usage:

This updated function can be used with various call notations:

• Positional Notation:

SELECT update_site('foo', 'New York');  -- no telephone

• Named Notation:

SELECT update_site(name => 'foo', _telephone => 123);  -- no city

• Mixed Notation:

SELECT update_site('foo', _telephone => 123);  -- still no city

Efficiency

Both approaches, using mode parameters or default values, can be efficient for simple update operations. However, for more complex scenarios, default values may provide a clearer and more maintainable solution.

Choice of Approach

The best choice zależy on specific requirements. If columns are defined as NOT NULL, default values offer a simpler and faster approach. For more complex scenarios involving SELECT queries with varying outputs, consider using VARIADIC or polymorphic input types and dynamic SQL.

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