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In mysql, you can use the ALTER TABLE statement to add fields and comments, which can add or modify data tables with the syntax "ALTER TABLE table name ADD field name type COMMENT 'comment content;"; ADD is used to add data, and COMMENT is used to represent the comment content.

The operating environment of this tutorial: windows10 system, mysql8.0.22 version, Dell G3 computer.

How to add fields and comments to mysql

Add field keyword alter comment keyword comment

The role of ALTER TABLE

The ALTER TABLE command is used to add, delete, or change columns in an existing data table.

The syntax is

ALTER TABLE table name ADD field name varchar (20) COMMENT 'comment content'

No comments, just get rid of comment

An example of adding fields is as follows:

Alter table user add COLUMN new1 VARCHAR (20) DEFAULT NULL; / / add a field, default is empty alter table user add COLUMN new2 VARCHAR (20) NOT NULL; / / add a field, default cannot be empty

If it is a table that has been built, you can use the command to modify the field, plus the comment attribute.

For example:

Alter table users modify name varchar (20) not null comment 'username'

Here users is the table name, name is the field name, varchar (20) is the type, and not null is the constraint.

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