How to delete and clean data in MySQL?

How to delete and clean data in MySQL?

When using MySQL database, data deletion and cleaning operations are very important, which can help us delete unnecessary data, optimize database performance, and release database storage space. This article will introduce how to use MySQL to delete and clean data, and provide corresponding code examples.

1. Delete data

1. DELETE statement

The DELETE statement is used to delete data in the table. It can delete records that meet the conditions according to specified conditions. .

Example 1: Delete records that meet the conditions in the table

DELETE FROM table_name WHERE condition;

Among them, table_name is the name of the table where data needs to be deleted, and condition is the condition for deleting data. For example, to delete records with age greater than or equal to 18 in the student table:

DELETE FROM student WHERE age >= 18;

2. TRUNCATE TABLE statement

The TRUNCATE TABLE statement is used to delete all data in the table and is more efficient than DELETE The statement is high, but it cannot contain a WHERE condition.

Example 2: Delete all data in the table

TRUNCATE TABLE table_name;

Among them, table_name is the name of the table whose data needs to be cleared. For example, clear all data in table student:

TRUNCATE TABLE student;

2. Cleanup operation

1. DROP DATABASE statement

DROP DATABASE statement is used to delete the entire database and all its tables and data.

Example 3: Delete database

DROP DATABASE database_name;

Among them, database_name is the name of the database that needs to be deleted. For example, delete the database named test:

DROP DATABASE test;

2. OPTIMIZE TABLE statement

OPTIMIZE TABLE statement is used to optimize the table and can clean up the fragments in the table to improve query speed and Storage space utilization.

Example 4: Optimizing table

OPTIMIZE TABLE table_name;

Among them, table_name is the name of the table that needs to be optimized. For example, optimizing table student:

OPTIMIZE TABLE student;

3. ALTER TABLE statement

ALTER TABLE statement can make structural modifications and adjustments to the table.

Example 5: Delete a field of the table

ALTER TABLE table_name DROP COLUMN column_name;

Among them, table_name is the name of the table where the field needs to be deleted, and column_name is the name of the field that needs to be deleted. For example, delete the field birthday in the student table:

ALTER TABLE student DROP COLUMN birthday;

The above is the method and sample code for data deletion and cleaning operations in MySQL. Please be careful when using it, especially when deleting data and tables, be sure to back up the data to avoid irreversible losses.

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