Modify mysql table structure

For developers who use MySQL to develop, modifying the data table structure is an inevitable process. Changes to the data table structure may include adding new fields, deleting useless fields, modifying field data types or data lengths, etc. This article will introduce how to modify the MySQL table structure.

Modify the table name

You can modify the table name through the RENAME operation, as shown below:

ALTER TABLE old_table RENAME new_table;

Add a new column

You can use the ALTER TABLE statement The ADD keyword in to add a new column, as shown below:

ALTER TABLE table_name ADD new_column_name data_type;

Note: The "data_type" here refers to the data type of the new column, which can be int, varchar, etc.

Delete columns

You can use the DROP keyword in the ALTER TABLE statement to delete columns, as shown below:

ALTER TABLE table_name DROP column_name;

Note: Deleting a column will affect the data in the table, Please proceed with caution.

Modify columns

You can use the MODIFY keyword in the ALTER TABLE statement to modify the data type and length of the column, as shown below:

ALTER TABLE table_name MODIFY column_name new_data_type(new_length);

Note: Modify the data of the column Type and length will also affect the data in the table, please proceed with caution.

Modify the column name

You can use the CHANGE keyword in the ALTER TABLE statement to modify the column name, as shown below:

ALTER TABLE table_name CHANGE old_column_name new_column_name data_type;

Modify the column position

You can use the FIRST and AFTER keywords in the ALTER TABLE statement to modify the position of the columns, as shown below:

ALTER TABLE table_name MODIFY column_name data_type FIRST;
ALTER TABLE table_name MODIFY column_name data_type AFTER another_column_name;

Note: If you use the FIRST keyword, the column will be moved to the first column, if you use the AFTER key word, the column will be moved after another column.

Modify the primary key

You can use the ADD and DROP keywords in the ALTER TABLE statement to add or delete the primary key, as shown below:

ALTER TABLE table_name ADD PRIMARY KEY (column_name);
ALTER TABLE table_name DROP PRIMARY KEY;

Modify the unique key

You can use the ADD and DROP keywords in the ALTER TABLE statement to add or delete unique keys, as follows:

ALTER TABLE table_name ADD UNIQUE (column_name);
ALTER TABLE table_name DROP INDEX unique_index_name;

Note: If you use the ADD keyword to add a unique key, you need to name the unique key.

Modify index

You can use the ADD, DROP and RENAME keywords in the ALTER TABLE statement to add, delete or rename indexes, as follows:

ALTER TABLE table_name ADD INDEX index_name (column_name);
ALTER TABLE table_name DROP INDEX index_name;
ALTER TABLE table_name RENAME INDEX old_index_name TO new_index_name;

Note: If you use the ADD keyword to add an index, you need to give the index a name.

Modify the self-growing column

You can use the AUTO_INCREMENT keyword in the ALTER TABLE statement to modify the starting value of the self-growing column, as follows:

ALTER TABLE table_name AUTO_INCREMENT = 100;

Modify the storage engine

You can use the ENGINE keyword in the ALTER TABLE statement to modify the storage engine, as shown below:

ALTER TABLE table_name ENGINE=InnoDB;

Note: Different storage engines support different functions and performance, and you need to be careful when switching storage engines. .

In short, modifying the MySQL table structure can be achieved through the ALTER TABLE statement, but it should be noted that the modification may have an impact on the data in the table. Please back up the data before operating.

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