mysql  default  constraint

the default constraint in MySQL is used to insert a default value into a column.

the default value is used if no value is specified for that field when inserting a record.

if no default modifier is specified on a field, mysql automatically assigns a default value depending on whether the field is null or not null.

mysql  default  constraint syntax:

     create table        table_name

                         column_name1   date_type(size)   default   value,
                         column_name2   date_type(size)   default   value,
                         column_name1   date_type(size)   default   value

MySQL Default Constraint Example

   create table      users

                      userid   not null,
                      firstname  text,
                      lastname  text,
                      salary float           default      0.0,
                      country      varchar(255)      default    'usa'

mysql default  constraint on alter table

to create a default constraint on the "country" column when the table is already created, use the following mysql statements:

                       alter  table      users

                       alter     country   set    default   'usa'

drop a  default constraint

to drop a default constraint, use the following mysql code:

                    alter  table  users

                    alter    country  drop   default