Creation of mysql stored procedure

MySQL stored procedure is an important feature of MySQL. It can encapsulate a set of SQL statements in a unit and can be used to complete certain operations and business logic processing.

Stored procedures can access data in the database, use SQL statements for process control, use conditional statements to handle errors, and so on. Using stored procedures can simplify the development and maintenance process of database applications and improve the reusability and maintainability of the program.

This article will introduce the basic concepts, creation methods, syntax structures and example applications of stored procedures.

1. Basic concepts

1. What is a stored procedure?

A stored procedure is a set of SQL statements that can be stored in the MySQL database. When these SQL statements need to be executed, the stored procedure can be called.

2. What is the role of stored procedures?

The stored procedure can encapsulate a set of commonly used SQL statements into a unit. When using it, you only need to call this unit, which can improve the performance, security and maintainability of the database.

3. What are the advantages of stored procedures?

(1) Excellent performance: Since the stored procedure is executed on the server side, it can reduce network transmission and data processing time and improve database performance.

(2) Safe and reliable: Stored procedures can achieve security management through permission control, which can prevent unauthorized users from accessing and modifying the database.

(3) High maintainability: Encapsulating frequently used SQL statements into stored procedures can improve code reusability and reduce the difficulty of program development and maintenance.

2. Creation method

Creating a stored procedure in MySQL is relatively simple. You only need to enter the CREATE PROCEDURE statement on the MySQL client.

CREATE PROCEDURE Stored procedure name (parameter list)
BEGIN

 SQL语句; 

END;

CREATE: Keyword to create a statement.

PROCEDURE: Indicates that the object to be created is a stored procedure.

Stored procedure name: The name of the created stored procedure.

Parameter list: Parameter list of the stored procedure. Parameters can be input parameters, output parameters, or a mixture of input and output parameters.

BEGIN and END: BEGIN and END are used to define the body of the stored procedure. Between BEGIN and END, you can define a set of SQL statements to implement the operations and business logic of the stored procedure.

3. Syntax structure

In the above example, we have introduced the basic syntax structure of the stored procedure. In addition to the CREATE PROCEDURE statement, stored procedures contain the following statements and components.

1. Parameter list

When creating a stored procedure, you can specify zero or more parameters to pass data to the stored procedure. The parameters of stored procedures can be divided into three categories.

(1) Input parameters: used to pass data to the stored procedure, which can only be read and cannot be modified in the stored procedure.

(2) Output parameters: used to return data from the stored procedure. After the stored procedure is executed, the data can be passed to the caller.

(3) Input/output parameters: Data can be passed as input parameters, or the processing results can be returned to the caller as output parameters.

When creating a stored procedure, you need to use parameter names, parameter types and parameter modifiers to define parameter types.

2. Variables

In a stored procedure, you can define local variables or global variables to store temporary data or calculation results.

Variable definition format:

DECLARE variable name data type [DEFAULT default value];

3. Control statement

In the stored procedure In , you can use control statements to implement process control, conditional judgment, exception handling, etc. Control statements include the following common operations.

(1) IF statement: used to perform conditional judgment and branch operations. The syntax format of the IF statement is:

IF condition THEN statement 1 ELSEIF condition THEN statement 2 ELSE statement 3 END IF;

(2) WHILE statement: used for loop processing. When a certain condition is met, a set of statements can be executed in a loop until the condition is not established or an exit condition is met, then the loop exits. The syntax format of the WHILE statement is:

WHILE conditional DO statement END WHILE;

(3) CASE statement: used for multi-condition analysis and branch selection, the syntax format of the CASE statement is:

CASE expression
WHEN value 1 THEN statement 1
WHEN value 2 THEN statement 2
. . .
ELSE statement n
END CASE;

( 4) Exception handling statements: used to handle exceptions. Commonly used exception handling statements include SIGNAL, RESIGNAL and HANDLER. For specific usage, please refer to the MySQL official documentation.

4. Example application

The following is a simple MySQL stored procedure example.

CREATE PROCEDURE GetStudent(IN id INT, OUT name VARCHAR(20))
BEGIN
SELECT student_name INTO name FROM student WHERE student_id = id;
END;

In this example, we created a stored procedure named GetStudent, which has two parameters: id and name, where id is an input parameter used to specify the student number to be queried, and name is an output parameter used to output the query. result.

In the body of the stored procedure, we use the SELECT statement to query the names of qualified students in the student table, store the query results in the variable name, and finally return the query results through the OUT keyword.

The method of using this stored procedure is as follows:

CALL GetStudent(1,@name);
SELECT @name;

In this example, we use CALL The statement calls the stored procedure GetStudent, passes the value of parameter id as 1, and defines a variable @name to store the query results. Finally, use the SELECT statement to output the query results.

5. Summary

MySQL stored procedures are an important feature of the MySQL database, which can help users encapsulate a set of commonly used SQL statements and improve the efficiency of database application development and maintenance. Creating MySQL stored procedures is very simple, you just need to follow the correct syntax format and naming rules.

In practical applications, stored procedures can help users implement complex business logic, improve program performance and security, and reduce data transmission and processing time. Users can flexibly use stored procedures to develop and maintain database applications according to their own needs and actual conditions.

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