mysql stored procedure returns

MySQL stored procedure return

MySQL stored procedure is a program that can be executed in the MySQL database. It can receive input parameters, perform a series of operations and return results. Unlike SQL statements, stored procedures can be precompiled and stored in the MySQL database, thereby improving program execution efficiency.

Stored procedures are usually used for complex business logic processing, which can reduce data transmission and processing time and improve execution efficiency. Stored procedures also provide better security and maintainability when developing applications.

MySQL stored procedures can return many types of results, including simple integers, strings, dates and times, as well as complex result sets. This article explains how to create a MySQL stored procedure and return results.

Create MySQL stored procedures

MySQL stored procedures can be created in the following ways:

CREATE PROCEDURE pro_name()
BEGIN    
    -- 存储过程的主体    
END；

Among them, pro_name is the name of the stored procedure, and between BEGIN and END is the stored procedure the subject.

The following is a simple stored procedure example, which can return the sum of two integers:

CREATE PROCEDURE add_numbers(IN a INT, IN b INT, OUT sum INT)
BEGIN
    SET sum = a + b;
END;

This stored procedure receives two integer parameters a and b, adds them and saves them into the sum variable. After the stored procedure is executed, the value of the sum variable will be returned.

Execute MySQL stored procedures

MySQL stored procedures can be executed in the following ways:

CALL pro_name();

Where pro_name is the name of the stored procedure to be executed. For the stored procedure in the above example, it can be executed in the following way:

CALL add_numbers(1, 2, @sum);
SELECT @sum;

The above code will call the add_numbers stored procedure, passing 1 and 2 as parameters to a and b, and the sum variable as the output parameter. Next, you can use a SELECT statement to get the value of the sum variable.

MySQL stored procedures return result sets

In addition to returning simple data types, MySQL stored procedures can also return result sets. A result set is a collection of data that can contain multiple rows and columns. MySQL stored procedures can use the following method to return the result set:

CREATE PROCEDURE pro_name()
BEGIN    
    SELECT columns FROM table WHERE condition;    
END；

where columns is the column name to be returned, table is the table name to be queried, and condition is the condition to be retrieved.

The following is an example of a stored procedure that returns a result set:

CREATE PROCEDURE get_users()
BEGIN
    SELECT * FROM users;
END;

This stored procedure will return all rows and columns in the users table. This stored procedure can be called with:

CALL get_users();

This will return all rows and columns in the users table.

MySQL stored procedure returns multiple result sets

MySQL stored procedure can also return multiple result sets. Multiple result sets are collections of data returned by one or more SELECT statements.

MySQL stored procedures can return multiple result sets in the following ways:

CREATE PROCEDURE pro_name()
BEGIN    
    SELECT columns FROM table WHERE condition;    
    SELECT columns FROM table WHERE condition;    
END；

Among them, columns is the column name to be returned, table is the table name to be queried, and condition is the condition to be retrieved. .

The following is an example of a stored procedure that returns multiple result sets:

CREATE PROCEDURE get_data()
BEGIN
    SELECT * FROM users;
    SELECT * FROM orders;
END;

This stored procedure will return all rows and columns in the users table and orders table. This stored procedure can be called by:

CALL get_data();

This will return the two result sets returned by the two SELECT statements.

MySQL stored procedures use conditional statements to return results

MySQL stored procedures can use conditional statements to return results. Conditional statements can use statements such as IF, CASE, and LOOP.

The following is an example of a stored procedure that uses an IF statement to return results:

CREATE PROCEDURE get_user_status(IN user_id INT, OUT status VARCHAR(255))
BEGIN
    DECLARE user_status INT;
    SELECT user_status INTO user_status FROM users WHERE id = user_id;
    
    IF user_status = 0 THEN
        SET status = 'Inactive';
    ELSEIF user_status = 1 THEN
        SET status = 'Active';
    ELSE
        SET status = 'Unknown';
    END IF;
END;

This stored procedure receives an integer parameter user_id and returns a string based on the user's status. The stored procedure first retrieves the user status corresponding to user_id from the users table and saves it in the user_status variable. Then use an IF statement to check the user status and set the value of the status variable. Finally, the stored procedure returns the status variable as an output parameter.

The above are some examples of results returned by MySQL stored procedures. Stored procedures are very powerful and useful tools in the MySQL database, which can handle complex business logic and improve the execution efficiency of applications. Appropriate stored procedures should be selected to process data based on specific business needs.

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