NULL can be specified in ALTER COLUMN to force a NOT NULL column to allow null values, except for columns in PRIMARY KEY constraints.NOT NULL can be specified in ALTER COLUMN only if the column contains no null values.
To change the collation of a user-defined alias data type column, you must execute separate ALTER TABLE statements to change the column to a SQL Server system data type and change its collation, and then change the column back to an alias data type.
ALTER COLUMN cannot have a collation change if one or more of the following conditions exist: For more information, see COLLATE (Transact-SQL).
Modifies a table definition by altering, adding, or dropping columns and constraints, reassigning and rebuilding partitions, or disabling or enabling constraints and triggers.
Transact-SQL Syntax Conventions Is the name of the table to be altered.
For a list and more information, see Windows Collation Name (Transact-SQL) and SQL Server Collation Name (Transact-SQL).
The COLLATE clause can be used to change the collations only of columns of the char, varchar, nchar, and nvarchar data types.
If the new column allows null values and a default definition is added with the new column, WITH VALUES can be used to store the default value in the new column for each existing row in the table.
If the new column does not allow null values and the table is not empty, a DEFAULT definition must be added with the new column, and the new column automatically loads with the default value in the new columns in each existing row.
If the table is not in the current database or is not contained by the schema owned by the current user, the database and schema must be explicitly specified.