You can create a rule and bind it to a column or user-defined datatype. Rules govern the kind of data that can or cannot be added.
For example, a rule called pub_idrule, which specifies acceptable publisher identification numbers, is bound to the pub_id column of the publishers table. The acceptable IDs are “1389,” “0736,” “0877,” “1622,” “1756,” or any four-digit number beginning with “99.” If you enter any other number, you see an error message.
When you get this kind of error message, you may want to use sp_helptext to look at the definition of the rule:
sp_helptext pub_idrule
---------
1
(1 row affected)
text
---------------------------------------------------
create rule pub_idrule
as @pub_id in ("1389", "0736", "0877", "1622", "1756")
or @pub_id like "99[0-9][0-9]"
(1 row affected)
For more general information on a specific rule, use sp_help, or, to find out if any of the columns has a rule, use sp_help with a table name as a parameter . See Chapter 14, “Defining Defaults and Rules for Data.”
