A column default can be specified using default constraints. The default constraint is used to insert a default value into a column. The default value will be added to all new record, if no other values is specified, including null.
Altering an existing column to add a default constraint
Syntax:-
Alter table table_name add constraint (constraints_name) default (default_value) for (existing column name)
Query:-
Alter table tblemployee add constraint df_tblgender_gnderid default 3 for genderId
NOTE
Tblemployee = table name
Df_tblgender_gnderid = default constraint
3= Default value
