ALTER TABLE - statement of language DB_MSSQL

ALTER TABLE table
  [ ADD column_name new_data_type [ NULL | NOT NULL ] [ PRIMARY KEY | UNIQUE ] [ IDENTITY ] [ DEFAULT default_expression ] [ CHECK check_expression ] [,...]
  [ DROP COLUMN column_name [, ...] ]
  [ ALTER COLUMN column_name new_data_type [ NULL | NOT NULL ]
  [, ...]
)

ALTER COLUMN	Alter existing table.
ADD	Adds new column.
DROP COLUMN	Delete existing column.
table	Name of the table.
column_name	Name of the column.
new_data_type	Column data type (bigint, int, smallint, tinyint, bit, decimal, numeric, money, smallmoney, float, real, datetime, smalldatetime, char, varchar, ntext, binary, varbinary, image).
NULL	Enable using the NULL value in the column.
NOT NULL	Disable using the NULL value in the column.
PRIMARY KEY	Specifies column as the primary key of the table (UNIQUE by default but UNIQUE mustn't be stated).
UNIQUE	Values in this column must be unique (writing the record with the value that already exists in this column, fails).
IDENTITY	Column (often primary key) whose unique value is supplied by the SQL server itself on writing (only 1 such column is enabled in the table).
DEFAULT	Definition of the default value, used on inserting new record, if the value for this column is not stated.
default_expression	the default value is is the result of this expression.
CHECK	On inserting or editing the value its check will be performed. If the check fails, then the whole operation fails.
check_expression	The check itself where the expression result specifies whether the operation is valid or not.