You can do it by edit of table design, if you want do it with query see following.
Syntax:
ALTER TABLE {TABLENAME}
ADD {COLUMNNAME} {TYPE} {NULL|NOT NULL}
CONSTRAINT {CONSTRAINT_NAME} DEFAULT {DEFAULT_VALUE}
[WITHVALUES]
Note: Use WITH VALUES to update existing null-able rows.
Example:
ALTERTABLE MyTable
ADD MyTableTypeID INTNOT NULL
CONSTRAINT Constraint_MyTableTypeID DEFAULT0
GO
Note: WITH VALUES handles the NOT NULL part
ALTERTABLE MyTable
ADD MyTableTypeID INT
CONSTRAINT Constraint_MyTableTypeID DEFAULT 0 WITH VALUE
GO