Column Definitions

Considerations for creating a column from a user-defined datatype.

You cannot change the length, precision, or scale.
You can use a NULL type to create a NOT NULL column, but not to create an IDENTITY column.
You can use a NOT NULL type to create a NULL column or an IDENTITY column.
You can use an IDENTITY type to create a NOT NULL column, but the column inherits the IDENTITY property. You cannot use an IDENTITY type to create a NULL column.

Only columns with variable-length datatypes can store null values. When you create a NULL column with a fixed-length datatype, the SAP ASE server automatically converts it to the corresponding variable-length datatype. The SAP ASE server does not inform the user of the type change.

This table lists the fixed-length datatypes and the variable-length datatypes to which they are converted. Certain variable-length datatypes, such as moneyn, are reserved types that cannot be used to create columns, variables, or parameters:

Variable-Length Datatypes Used to Store Nulls
Original Fixed-Length Datatype	Converted to
`char`	`varchar`
`nchar`	`nvarchar`
`binary`	`varbinary`
`datetime`	`datetimn`
`float`	`floatn`
`bigint`, `int`, `smallint`, `tinyint`	`intn`
`unsigned bigint, unsigned int, unsigned smallint`	`uintn`
`decimal`	`decimaln`
`numeric`	`numericn`
`money` and `smallmoney`	`moneyn`

For a report on a table and its columns, execute the system procedure sp_help.

You can create column defaults in two ways: by declaring the default as a column constraint in the create table or alter table statement, or by creating the default using the create default statement and binding it to a column using sp_bindefault.