The normal syntax to call another PL/pgSQL function from within PL/pgSQL is to either reference the function in a SQL
SELECT statement, or during the assignment of a variable. For example:
The use of assignments and SELECT statements to execute functions is standard in
PL/pgSQL because all functions in a PostgreSQL database
return a value of some type. Use the
PERFORM keyword to call a function and ignore its return data. Example 11-50 shows the syntax of the PERFORM keyword.
Example 11-50. Syntax of the PERFORM keyword
Example 11-51 demonstrates the use of PERFORM to invoke a
PL/pgSQL function, and shows how to call another PL/pgSQL function through assignment (via a
SELECT INTO statement). The ship_item function is a
useful wrapper to the add_shipment function. It accepts basic information, makes sure
the customer and book both exist, and then sends the information to add_shipment.
Example 11-51. Using the PERFORM keyword
CREATE FUNCTION ship_item (text,text,text) RETURNS integer AS '
-- Declare function argument aliases.
l_name ALIAS FOR $1;
f_name ALIAS FOR $2;
book_isbn ALIAS FOR $3;
-- Declare a variable to hold the book ID number. This variable
-- is necessary to check for the existence of the provided ISBN.
-- Declare a variable to hold the customer ID number. This variable
-- is necessary to check for the existence of the customer.
-- Retrieve the customer ID number with a previously created
SELECT INTO customer_id get_customer_id(l_name,f_name);
-- If the customer does not exist, return -1 and exit. The
-- get_customer_id function returns a -1 if the customer is not found.
IF customer_id = -1 THEN
-- Retrieve the ID number of the book with the specified ISBN.
SELECT INTO book_id book_id FROM editions WHERE isbn = book_isbn;
-- If the book does not exist in the system, return a -1.
IF NOT FOUND THEN
-- If the book and customer both exist, add the shipment.
-- Return 1 to indicate the function was successful.
' LANGUAGE 'plpgsql';