A positional parameter reference is typically used in a SQL function definition statement to indicate a parameter in a SQL function. The syntax to specify a parameter is:



Where ## acts as the index position of the parameter you are searching for. For example, the following function returns the title of a book when passed the isbn number.

Example 4-47. Creating a Function

booktown=# CREATE FUNCTION isbn_to_title(text) RETURNS text
booktown-#     AS 'SELECT title from books where isbn = $1' 
booktown-#       LANGUAGE 'sql';

The $1 in the function definition is substituted with the first function argument when the function is called.

Note Function List in psql

Remember that to see a list of PostgreSQL's built-in functions, you may use the psql command \df .

If you want to delete your function after having created it, use the DELETE FUNCTION command. This command takes in the function name and type. Like this:

   DELETE FUNCTION funcName(type); 

If the inventory function was not needed anymore, then we can delete it using the command:

Example 4-48. Removing a Function

    DELETE FUNCTION inventory(integer);