mysql statement stored procedure

MySQL is one of the most widely used relational database management systems in the world, and stored procedures are a very important function in MySQL. Stored procedures are a collection of precompiled SQL statements that provide us with a simple and powerful development and maintenance method. In this article, we will learn how to use MySQL statements and stored procedures.

MySQL statement

SQL statement is a language for interacting with relational databases, and MySQL is no exception. The following are some basic MySQL statements:

1. Create database: CREATE DATABASE ;
2. Delete database: DROP DATABASE ;
3. Display All databases: SHOW DATABASES;
4. Select database: USE ;
5. Create table: CREATE TABLE （column1 datatype(length), column2 datatype(length).. .);
6. Delete table: DROP TABLE ;
7. Insert data: INSERT INTO (column1, column2...) VALUES (value1, value2... );
8. Delete data: DELETE FROM WHERE ;
9. Modify data: UPDATE SET column1=value1, column2=value2... WHERE < ;conditions>;

The above are some basic MySQL statements, but in actual development, we need to be familiar with and master more operations.

Stored procedure

Stored procedure is an important advanced feature in MySQL. A stored procedure is a program composed of SQL statements and operational logic. It can accept parameters, perform specific tasks, and output return values. The biggest advantage of stored procedures is that they can be reused, allowing code reuse and maintenance.

The following is an example of a stored procedure:

CREATE PROCEDURE sp_get_users(IN p_user_id INT)
BEGIN

SELECT * FROM users WHERE user_id = p_user_id;

END;

In this storage During the process, we defined an input parameter p_user_id to accept the user ID. We then use a SELECT statement to query the users table for rows that match the user ID and return the results. In this way, we can use this stored procedure to call it directly in other scenarios where user information needs to be queried.

Stored procedures can not only query data, but also implement operations such as update, delete, and insert. The following is an example of a stored procedure for an update operation:

CREATE PROCEDURE sp_update_user(IN p_user_id INT, IN p_user_name VARCHAR(50))
BEGIN

UPDATE users SET user_name = p_user_name WHERE user_id = p_user_id;

END;

In this stored procedure, we define two input parameters p_user_id and p_user_name to accept user ID and user name. We then use an UPDATE statement to update the row in the users table that matches that user ID and update the user name to p_user_name.

In addition to input parameters, stored procedures can also accept output parameters. The following is an example:

CREATE PROCEDURE sp_get_user_count(OUT p_user_count INT)
BEGIN

SELECT COUNT(*) INTO p_user_count FROM users;

END;

In this stored procedure, we define an output parameter p_user_count, used to output the total number of users. Then, we use the SELECT COUNT(*) statement to query the total number of rows in the users table and assign it to the p_user_count parameter.

Summary

MySQL statements and stored procedures are two important features in MySQL that developers must master proficiently. SQL statements can perform basic operations on data, while stored procedures provide more advanced and complex functions. In development, it is often necessary to flexibly apply these features according to actual business scenarios in order to maximize their benefits.

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