- Create Stored Procedures
- Execute or Call Stored Procedures
- Use Parameters (IN, OUT, and INOUT)
- Drop Stored Procedure
To call a stored procedure in MySQL, you typically use the
CALL statement. Here’s the basic syntax:
procedure_name with the name of your stored procedure, and provide any required arguments based on the definition of the procedure. Let’s first create a stored procedure to fully understand the concept.
Create a Stored Procedure
To create a stored procedure, you need two things: a code editor to write the code for the stored procedure e.g. Notepad or Sublime Text, and a tool that sends the code to the MySQL/MariaDB server and creates the stored procedure. There are several options for compiling your code, such as:
- MySQL command-line client:
You can interact with it directly through your terminal or command prompt.
- MySQL Workbench:
It offers a user-friendly interface for creating, editing, and running SQL codes (only supports MySQL).
- HeidiSQL (or another third-party tool):
Similar to MySQL Workbench, it supports MariaDB, MySQL, Microsoft SQL, PostgreSQL, and SQLite.
To begin this tutorial, we’ll use the MySQL command-line client, which is a common tool that comes with the MySQL server (and XAMPP) installation. To access the MySQL server on your local machine using port
3306 and the
root user, follow these steps:
- Launch the command prompt/terminal on your computer
- Navigate to the mysql installation directory and then to the
mysql -u root -pand hit enter.
- Enter the password when prompted.
::Connecting to the MySQL command-line client D:\xampp\mysql\bin>mysql -u root -p Enter password: Welcome to the MariaDB monitor. Commands end with ; or \g. Your MariaDB connection id is 10 Server version: 10.4.24-MariaDB mariadb.org binary distribution Copyright (c) 2000, 2018, Oracle, MariaDB Corporation Ab and others. Type 'help;' or '\h' for help. Type '\c' to clear the current input statement. MariaDB>
To create a procedure in MySQL, you use the
CREATE PROCEDURE statement followed by the procedure’s name, parameter list (if any), and the SQL statements that constitute the procedure’s body. Here’s the syntax for creating a stored procedure in MySQL:
CREATE PROCEDURE [IF NOT EXISTS] procedure_name( [IN parameter1 data_type, OUT parameter2 data_type, INOUT parameter3 data type...]) BEGIN -- SQL statements for the stored procedure's logic END
IF NOT EXISTS(optional) prevents an error from occurring if a procedure with the same name exists.
IN(default) parameter passes a value into a procedure.
OUTparameter passes a value from the procedure back to the caller.
INOUTparameter passes a value into the procedure and any changes made by the procedure pass back to the caller.
Let’s create a simple stored procedure that returns the average product price. Here’s an example of creating a procedure.
-- Creating a simple procedure CREATE PROCEDURE itempricing() BEGIN SELECT Avg(price) AS priceaverage FROM products; END;
The stored procedure is named
itempricing and is thus defined with the statement
CREATE PROCEDURE itempricing(). This stored procedure has no parameters, but the trailing
() is still required.
END statements are used to delimit the stored procedure body, and the body itself is just a simple
MySQL Command-line Client Delimiters
If you are using the mysql command-line utility, pay careful attention to this section.
The default MySQL statement delimiter is
; (as you have seen in all of the MySQL statements used thus far). However, the mysql command-line utility also uses
; as a 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.
The solution is to temporarily change the command-line utility delimiter from
//, as shown in the above example:
-- Creating a simple procedure DELIMITER // CREATE PROCEDURE itempricing() BEGIN SELECT Avg(price) AS priceaverage FROM products; END// DELIMITER ;
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;. This way the
; within the stored procedure body remains intact and is correctly passed to the database engine. And then, to restore things back to how they were initially, the statement closes with a
Any character can be used as the delimiter except for the
Executing or Calling Stored Procedures
MySQL refers to stored procedure execution as calling, and so the MySQL statement to execute a stored procedure is simply
CALL takes the name of the stored procedure and any parameters that need to be passed to it. So how would you use this stored procedure? Like this
CALL itempricing(); +--------------+ | priceaverage | +--------------+ | 18.75 | +--------------+
CALL itempricing(); executes the just-created stored procedure and displays the returned result. 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).
itempricing is a really simple stored procedure it simply displays the results of a
SELECT statement. Typically stored procedures do not display results; rather, they return them into variables that you specify.
Here is an updated version of
itempricing (you’ll not be able to create the stored procedure again if you did not previously drop it):
DELIMITER // CREATE PROCEDURE itempricing( OUT pl DECIMAL(8,2), OUT ph DECIMAL(8,2), OUT pa DECIMAL(8,2) ) BEGIN SELECT Min(price) INTO pl FROM products; SELECT Max(price) INTO ph FROM products; SELECT Avg(price) INTO pa FROM products; END// DELIMITER;
This stored procedure accepts three parameters:
plto store the lowest product price,
phto store the highest product price, and
pato store the average product price (and thus the variable names).
Each parameter must have its type specified; here a decimal value is used. 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).
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 stored procedure code itself is enclosed within
END statements as seen before, and a series of
SELECT statements are performed to retrieve the values that are then saved into the appropriate variables (by specifying the
The datatypes allowed in stored procedure parameters are the same as those used in tables.
Note that a recordset is not an allowed type, and so multiple rows and columns could not be returned via a parameter. This is why three parameters (and three
SELECT statements) are used in the previous example.
To call this updated stored procedure, three variable names must be specified, as seen here (Note: All MySQL variable names must begin with
CALL itempricing(@pricelow, @pricehigh, @priceaverage);
As the stored procedure expects three parameters, exactly three parameters must be passed, no more and no less. Therefore, three parameters are passed to this
CALL statement. These are the names of the three variables that the stored procedure will store the results in.
When called, this statement does not actually display any data. Rather, it returns variables that can then be displayed (or used in other processing).
To display the retrieved average product price you could do the following:
CALL itempricing(@pricelow, @pricehigh, @priceaverage); SELECT @priceaverage; +---------------+ | @priceaverage | +---------------+ | 16.133571428 | +---------------+
To obtain all three values, you can use the following:
CALL itempricing(@pricelow, @pricehigh, @priceaverage); SELECT @pricehigh, @pricelow, @priceaverage; +------------+-----------+---------------+ | @pricehigh | @pricelow | @priceaverage | +------------+-----------+---------------+ | 55.00 | 2.50 | 16.133571428 | +------------+-----------+---------------+
Here is another example, this time using both
ordertotal accepts an order number and returns the total for that order:
DELIMITER // CREATE PROCEDURE ordertotal( IN onumber INT, OUT ototal DECIMAL(8,2) ) BEGIN SELECT Sum(item_price*quantity) FROM orderitems WHERE order_num = onumber INTO ototal; END// DELIMITER ;
onumber is defined as
IN because the order number is passed in to the stored procedure.
ototal is defined as
OUT because the total is to be returned from the stored procedure. The
SELECT statement used both of these parameters, the
WHERE clause uses
onumber to select the right rows, and
ototal to store the calculated total.
To invoke this new stored procedure you can use the following:
CALL ordertotal(25, @total);
Two parameters must be passed to
ordertotal; the first is the order number and the second is the name of the variable that will contain the calculated total.
To display the total you can then do the following:
SELECT @total; +--------+ | @total | +--------+ | 160.50 | +--------+
@total has already been populated by the
CALL statement to
SELECT displays the value it contains.
To obtain a display for the total of another order, you would need to call the stored procedure again, and then redisplay the variable:
CALL ordertotal(29, @total); SELECT @total; +--------+ | @total | +--------+ | 180.00 | +--------+
INOUT parameters allow you to pass a value into a stored procedure and return a modified value after the procedure execution.
Let’s say you want to create a stored procedure that increments a given number by a specified value and returns the updated result.
-- Create a stored procedure with an INOUT parameter DELIMITER // CREATE PROCEDURE IncrementNumber( INOUT num INT, IN increment_value INT) BEGIN SET num = num + increment_value; END // DELIMITER ;
Calling the stored procedure with the
SET @input_number = 10; SET @increment_value = 5; -- Call the stored procedure with INOUT parameter CALL IncrementNumber(@input_number, @increment_value); -- The @input_number variable now holds the updated value SELECT @input_number;
This example demonstrates how to create and use an INOUT parameter in a MySQL stored procedure to modify a variable’s value and return the updated result.
Dropping Stored Procedures
After stored procedures are created, they remain on the server, ready for use, until dropped. The
drop command removes the stored procedure from the server.
To remove the stored procedure we just created, use the following statement:
DROP PROCEDURE itempricing;
This removes the just-created stored procedure. Notice that the trailing
() is not used; here just the stored procedure name is specified.
DROP PROCEDURE will throw an error if the named procedure does not actually exist. To delete a procedure if it exists (and not throw an error if it does not), use:
DROP PROCEDURE IF EXISTS