Sybase 12.4.2 User Manual

CHAPTER 7    Ensuring Data Integrity

By default, string comparisons are case insensitive unless the database is 
explicitly created as a case-sensitive database, using the 

CASE RESPECT

 

option.

Example 3

You can specify that a date or number falls in a particular range. For example, 
you may want to require that the 

start_date

 column of an employee table must 

be between the date the organization was formed and the current date, as in the 
following:

ALTER TABLE employee

MODIFY start_date

CHECK ( start_date BETWEEN ’1983/06/27’

                   AND CURRENT DATE ) UNENFORCED

You can use several date formats: the YYYY/MM/DD format used in this 
example has the virtue of always being recognized regardless of the current 
option settings.

You can attach unenforced CHECK conditions to user-defined data types. 
Columns defined on those data types inherit the CHECK conditions. A 
CHECK condition explicitly specified for the column overrides that from the 
user-defined data type.

When defining a CHECK condition on a user-defined data type, any variable 
prefixed with the @ sign is replaced by the name of the column when the 
CHECK condition is evaluated. For example, the following user-defined data 
type accepts only positive integers:

CREATE DATATYPE posint INT

CHECK ( @col > 0 ) UNENFORCED

Any variable name prefixed with @ could be used instead of 

@col

. Any 

column defined using the 

posint

 data type accepts only positive integers unless 

it has a CHECK condition explicitly specified.

An ALTER TABLE statement with the DELETE CHECK clause deletes all 
CHECK conditions from the table definition, including those inherited from 
user-defined data types.

For information on user-defined data types, see “User-defined data types” in 
the Adaptive Server IQ Reference.