![]() ![]() MySQL supports parameters of types IN (those passed to stored procedures), OUT (those passed from stored procedures, as we've used here), and INOUT (those used to pass parameters to and from stored procedures). ![]() The keyword OUT is used to specify that this parameter is used to send a value out of the stored procedure (back to the caller). Each parameter must have its type specified here a decimal value is used. This stored procedure accepts three parameters: pl to store the lowest product price, ph to store the highest product price, and pa to store the average product price (and thus the variable names). Here is an updated version of productpricing (you'll not be able to create the stored procedure again if you did not previously drop it): CREATE PROCEDURE productpricing( Variable A named location in memory, used for temporary storage of data. Typically stored procedures do not display results rather, they return them into variables that you specify. Productpricing is a really simple stored procedureit simply displays the results of a SELECT statement. To delete a procedure if it exists (and not throw an error if it does not), use DROP PROCEDURE IF EXISTS. Notice that the trailing () is not used here just the stored procedure name is specified.ĭrop Only If It Exists DROP PROCEDURE will throw an error if the named procedure does not actually exist. This removes the just-created stored procedure. To remove the stored procedure we just created, use the following statement: DROP PROCEDURE productpricing The drop command removes the stored procedure from the server. Dropping Stored ProceduresĪfter they are created, stored procedures remain on the server, ready for use, until dropped. As a stored procedure is actually a type of function, () characters are required after the stored procedure name (even when no parameters are being passed). So how would you use this stored procedure? Like this: CALL productpricing() ĬALL productpricing() executes the just-created stored procedure and displays the returned result. If you are using the mysql command-line utility, keep this in mind as you work through this tutorial. Īny character may be used as the delimiter except for \. And then, to restore things back to how they were initially, the statement closes with a DELIMITER. This way the within the stored procedure body remains intact and is correctly passed to the database engine. Here, DELIMITER // tells the command-line utility to use // as the new end of statement delimiter, and you will notice that the END that closes the stored procedure is defined as END // instead of the expected END. The solution is to temporarily change the command-line utility delimiter, as seen here: DELIMITER // If the command-line utility were to interpret the characters inside of the stored procedure itself, those would not end up becoming part of the stored procedure, and that would make the SQL in the stored procedure syntactically invalid. However, the mysql command-line utility also uses as a delimiter. The default MySQL statement delimiter is (as you have seen in all of the MySQL statement used thus far). Mysql Command-line Client Delimiters If you are using the mysql command-line utility, pay careful attention to this note. No data is returned because the code does not call the stored procedure, it simply creates it for future use. When MySQL processes this code it creates a new stored procedure named productpricing. BEGIN and END statements are used to delimit the stored procedure body, and the body itself is just a simple SELECT statement. This stored procedure has no parameters, but the trailing () is still required. Had the stored procedure accepted parameters, these would have been enumerated between the ( and ). The stored procedure is named productpricing and is thus defined with the statement CREATE PROCEDURE productpricing(). Ignore the first and last lines for a moment we'll come back to them shortly. Here is the code: CREATE PROCEDURE productpricing() To give you a taste for what is involved, let's look at a simple examplea stored procedure that returns the average product price. Creating Stored ProceduresĪs already explained, writing a stored procedure is not trivial. Stored procedures might or might not display results, as you will see shortly. Take a look at this example: CALL a stored procedure named productpricing is executed it calculates and returns the lowest, highest, and average product prices. ![]() CALL takes the name of the stored procedure and any parameters that need to be passed to it. MySQL refers to stored procedure execution as calling, and so the MySQL statement to execute a stored procedure is simply CALL. ![]()
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