mysql command modification

MySQL is a popular relational database management system that is widely used to develop and manage large databases. It provides a variety of powerful commands and functions to manage and operate databases. In this article, we will focus on some common commands in MySQL, focusing on how to use MySQL commands to modify the database.

In MySQL, you can use many commands to modify the database and other objects, such as tables, views, triggers, etc. Some commonly used MySQL commands will be introduced in detail below.

1. Modify the table name

In MySQL, you can use the following command to modify the table name:

ALTER TABLE table_name RENAME TO new_table_name;

Where, table_name represents the table name to be modified , new_table_name represents the new table name to be modified.

For example, to change the table name from "students" to "new_students", you can use the following command:

ALTER TABLE students RENAME TO new_students;

2. Add and delete columns

In MySQL, we can use the following command to change the columns of the table:

ALTER TABLE table_name ADD COLUMN column_name column_definition AFTER existing_column;

Among them, table_name represents the table name to be modified, column_name represents the column name to be added or deleted, and column_definition represents the type of column to be added. and attribute, AFTER existing_column indicates that the column should be inserted at the location of the existing column.

For example, to add an "address" column in the "students" table, you can use the following command:

ALTER TABLE students ADD COLUMN address VARCHAR(100) AFTER name;

To delete the "address" column in the "students" table, you can Use the following command:

ALTER TABLE students DROP COLUMN address;

3. Modify column type

In MySQL, you can use the following command to change the data type of a column to a new type:

ALTER TABLE table_name MODIFY COLUMN column_name new_data_type;

Among them, table_name represents the table name to be modified, column_name represents the column name of the data type to be modified, and new_data_type represents the new data type.

For example, to change the "age" column in the "students" table from INT to VARCHAR, you can use the following command:

ALTER TABLE students MODIFY COLUMN age VARCHAR(50);

4. Modify the column name

In MySQL, you can use the following command to change the column name to a new name:

ALTER TABLE table_name CHANGE COLUMN old_column_name new_column_name column_definition;

Among them, table_name represents the table name to be modified, old_column_name represents the column name to be renamed, new_column_name represents the new column name, column_definition Indicates the definition of the column.

For example, to change the "name" column name in the "students" table to "full_name", you can use the following command:

ALTER TABLE students CHANGE COLUMN name full_name VARCHAR(100);

5. Add and delete indexes

In MySQL, you can use the following command to add an index to a table:

ALTER TABLE table_name ADD INDEX index_name (column_name);

Among them, table_name represents the name of the table to be added as an index, index_name represents the name of the index to be added, and column_name represents the column to be added as an index. name.

For example, to add the "age" column of the "students" table as an index, you can use the following command:

ALTER TABLE students ADD INDEX age_index (age);

To delete the index, you can use the following command:

ALTER TABLE students DROP INDEX age_index;

6. Modify the table engine type

In MySQL, you can use the following command to change the engine type of the table to a new engine type:

ALTER TABLE table_name ENGINE = new_engine_type;

Among them, table_name means to modify The table name, new_engine_type indicates the new engine type to be changed to, such as MyISAM, InnoDB, etc.

For example, to change the engine type of the "students" table from InnoDB to MyISAM, you can use the following command:

ALTER TABLE students ENGINE = MyISAM;

In this article, we introduce some commonly used MySQL commands, which can be used Used to modify databases and other objects, including tables, views, indexes, etc. By using these commands, developers can manage and operate the database more conveniently. These commands are the core functions of MySQL, and users should be familiar with them and master their use.

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