MySql adds and deletes fields, modifies field names, and modifies field types.

MySql adds and deletes fields, modifies field names, and modifies simple syntax of the field type MySql, which is commonly used but not easy to remember. Of course, these SQL syntaxes are basically common in various databases. Listed below: 1. add a field alter table user add COLUMN new1 VARCHAR (20) default null; // add a field. The DEFAULT value is alter table user add COLUMN new2 VARCHAR (20) not null; // Add a field. The default value cannot be www.2cto.com 2. delete a field alter table user drop column new2; // delete a field 3. MODIFY a field alter table user MODIFY new1 VARCHAR (10); // MODIFY the type of a field alter table user CHANGE new1 new4 int; // MODIFY the name of a field, in this case, you must specify the field type again.