delete row mysql

MySQL database management system is a widely used relational database, which provides a rich set of SQL statements and commands for operating the database. Among them, the DELETE command is a common operation that can be used to delete rows in one or more tables. This article will introduce the methods, precautions and practical applications of deleting rows in MySQL.

1. MySQL row deletion syntax

In MySQL, the syntax for deleting rows is as follows:

DELETE FROM table_name WHERE condition(s);

Among them, table_name is the name of the table to delete rows, and condition(s) is To filter out the conditions for rows to be deleted, you can use AND or OR to connect multiple conditions.

For example, to delete the row with the middle school number 1001 in the table named student, you can use the following statement:

DELETE FROM student WHERE s_id = 1001;

2. Notes on deleting rows in MySQL

1. Use with caution, the deletion operation is irreversible.

The deletion operation is irreversible, so before performing the deletion operation, be sure to confirm whether the data to be deleted is correct. Generally speaking, it is best to use the SELECT statement to check whether the data to be deleted is as expected, and then execute the DELETE command.

SELECT * FROM student WHERE s_id = 1001;
DELETE FROM student WHERE s_id = 1001;

2. The conditions in the WHERE clause must be unique.

If the conditions in the WHERE clause are not unique, multiple rows of data will be deleted. Therefore, when using the DELETE command, you should select appropriate filtering conditions based on data characteristics and needs to avoid accidentally deleting data.

DELETE FROM student WHERE s_name = '张三';

3. The deletion operation will trigger related constraints and triggers.

If foreign key constraints and triggers are involved in the deletion operation, the system will automatically trigger the relevant constraints and triggers and perform integrity checks. If integrity rules are violated during the deletion operation, the deletion operation will be terminated and relevant error information will be returned.

4. The deletion operation will occupy system resources and affect performance.

When performing a large number of deletion operations, system resources may be occupied, affecting system performance and user experience. Therefore, the appropriate deletion strategy should be selected based on the specific situation to reduce the resources occupied by the deletion operation as much as possible and improve the deletion efficiency.

3. Example applications of deleting rows in MySQL

The following introduces some example applications of deleting rows in MySQL.

1. Delete empty tables

If a table no longer has valid data, you can use the DELETE command to delete all rows to clear the table. For example, to delete all rows in the table named student, you can use the following statement:

DELETE FROM student;

2. Delete part of the data that meets the conditions

If you want to delete the data in the table that meets a specific Conditional data can be filtered using the WHERE clause. For example, to delete all male student data in the table named student, you can use the following statement:

DELETE FROM student WHERE s_gender = 'M';

3. Delete a large amount of data

If you want to delete the Large amounts of data can be deleted in batches to avoid occupying too many system resources. For example, to delete all failed student data in the table named student by deleting 1,000 rows at a time, you can use the following statement:

WHILE (SELECT COUNT(*) FROM student WHERE s_score < 60) > 0
DO
    DELETE FROM student WHERE s_score < 60 LIMIT 1000;
END WHILE;

4. Delete duplicate data in the table

If there is duplicate data in the table, you can use the DELETE and ORDER BY statements to delete the duplicate data. For example, to delete duplicate student data in a table named student, you can use the following statement:

DELETE FROM student
WHERE s_id NOT IN
(
    SELECT MAX(s_id) FROM student GROUP BY s_name, s_gender, s_age
);

The above is an introduction to the methods, precautions and example applications of deleting rows in MySQL. In actual use, appropriate deletion strategies should be adopted based on specific circumstances to avoid accidentally deleting data and improve system performance and user experience.

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