Attribute annotations

Tagged values

The tagged values specific to Sybase available at attribute level are presented in the following table:

The ... tagged value	is used to ...	Sybase
{default}	give the default value in the column	DEFAULT
{check}	declare a "check" type constraint in the column associated to the attribute in question.	CHECK
{null}	specify that the column is NULL type	NULL
{unique}	declare the column as unique	UNIQUE

The {check} tagged value

The {check} tagged value allows the specification of a Boolean expression in a column, that will have to be checked in order that a tuple be inserted in the table.

The name of the column in question must appear in the expression and must be the only one.

See the {check} tagged value on classes for further details.

The {null} tagged value

This tagged value imposes the generation of a "NULL" constraint in the column corresponding to the attribute.

This constraint allows the use of an "undetermined" when inserting a tuple for which data has not been entered in the column.

The {unique} tagged value

This tagged value is used to specify that all the values of the column are unique.