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.
The pub_id column of the publishers table is an example. A rule called pub_idrule, which specifies acceptable publisher identification numbers, is bound to the column. The acceptable IDs are “1389”, “0736”, “0877”, “1622”, and “1756” or any four-digit number beginning with “99”. If you enter any other number, you get 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 use sp_help with a table name as a parameter to find out if any of the columns has a rule. See Chapter 13, “Defining Defaults and Rules for Data.”
