The principle and implementation method of MySQL paging stored procedure

MySQL is a very popular open source relational database management system. When using MySQL for data query, if faced with massive data, in order to improve efficiency and performance, paging technology is usually used for data display.

MySQL provides a variety of implementation methods for paging, among which stored procedures are a very common implementation method. This article will introduce the principles and specific implementation methods of MySQL paging stored procedures.

1. Paging Principle

Data paging in MySQL is actually to obtain the corresponding data from the entire data set based on the specified number of data items per page and the current page number.

For the situation where M pieces of data are required to be obtained on page N, the commonly used paging algorithm is implemented by using LIMIT and OFFSET statements. LIMIT is a statement in MySQL used to specify how many pieces of data to retrieve, and OFFSET is used to specify which record to start fetching data from.

For example, when the user requests page 3 and each page displays 10 pieces of data, the following SQL statement can be used to obtain the data:

SELECT * FROM table LIMIT 10 OFFSET 20

Among them, LIMIT 10 means that the number of data items per page is 10, and OFFSET 20 means starting to obtain the 20th piece of data.

2. Stored procedures implement paging

In MySQL, a stored procedure is a preprocessed database object that can accept parameters and perform a series of operations. Therefore, we can implement MySQL paging queries through stored procedures.

The implementation idea is as follows:

1. Accept parameters: the number of impressions per page and the current page number
2. Calculate the offset offset and based on the number of impressions per page and the current page number Data quantity limit
3. Construct and execute SQL query statements to obtain the data of the corresponding page
4. Return query results

The following code example implements a MySQL paging stored procedure:

DELIMITER $
CREATE PROCEDURE page_query(

cur_page INT,
page_size INT

)
BEGIN

DECLARE start_page INT DEFAULT 0;
DECLARE offset_size INT DEFAULT 0;
SET start_page = cur_page * page_size;
SET offset_size = page_size;
SET @sql = CONCAT('SELECT * FROM `table` LIMIT ', start_page, ',', offset_size);
PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

END$
DELIMITER ;

In the above code, we first use DELIMITER to define the statement end character as $ to prevent the interference of semicolons in SQL statements.

Then use CREATE PROCEDURE to define the parameter list and implementation logic of the stored procedure. Pass cur_page and page_size as parameters into the stored procedure.

Then, we defined two variables start_page and offset_size, which are used to calculate the starting position of our query and the number of records to be queried respectively.

Finally, we use the CONCAT function to construct a SQL query statement, in which start_page and offset_size in the LIMIT statement are the paging parameters we calculated earlier.

Next, we use the PREPARE statement to preprocess the constructed query statement, and execute the QUERY statement to obtain the data.

Finally, we use the DEALLOCATE PREPARE statement to release the prepared SQL statement.

3. Use stored procedures to implement paging queries

It is very simple to use the MySQL paging stored procedures just defined. We only need to pass in the number of data displayed on each page and the current page number to obtain the corresponding page of data.

For example, to obtain page 2 and display 5 pieces of data on each page, you can use the following SQL statement:

CALL page_query(2, 5)

This stored procedure call Data items 6-10 of the result table will be returned.

4. Summary

Using stored procedures to implement the paging function in MySQL is a very efficient and flexible way, which can effectively improve the query efficiency and response speed when querying large amounts of data. At the same time, stored procedures can ensure data security and avoid security issues such as SQL injection. Through this article, we can understand the basic principles of MySQL paging implementation and the method of using stored procedures to implement MySQL paging queries.

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