SQL/PSM Stored Procedures Basic PSM Form Parameters In
Stored Procedures PSM, or “persistent, stored modules,” SQL/PSM allows us to store procedures as database schema elements. PSM = a mixture of conventional Procedures Stored in the Database statements (if, while, etc.) and SQL. General-Purpose Programming Lets us do things we cannot do in SQL alone. 1 2 Basic PSM Form Parameters in PSM CREATE PROCEDURE <name> ( Unlike the usual name-type pairs in <parameter list> ) languages like C, PSM uses mode- <optional local declarations> name-type triples, where the mode can be: <body>; IN = procedure uses value, does not Function alternative: change value. CREATE FUNCTION <name> ( OUT = procedure changes, does not use. <parameter list> ) RETURNS <type> INOUT = both. 3 4 1 Example: Stored Procedure The Procedure Let’s write a procedure that takes two CREATE PROCEDURE JoeMenu ( arguments b and p, and adds a tuple IN b CHAR(20), Parameters are both to Sells(bar, beer, price) that has bar = IN p REAL read-only, not changed ’Joe’’s Bar’, beer = b, and price = p. ) Used by Joe to add to his menu more easily. INSERT INTO Sells The body --- VALUES(’Joe’’s Bar’, b, p); a single insertion 5 6 Invoking Procedures Types of PSM statements --- (1) Use SQL/PSM statement CALL, with the RETURN <expression> sets the return name of the desired procedure and value of a function. arguments. Unlike C, etc., RETURN does not terminate Example: function execution. CALL JoeMenu(’Moosedrool’, 5.00); DECLARE <name> <type> used to declare local variables. Functions used in SQL expressions wherever a value of their return type is appropriate.
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