Introduction To SQLUnit 8

Modern Business Technology

Introduction To TSQLUnit 8

Developed by

Michael Hotek

Defaults

• A default can exist as a separate object

• A default still follows the same rules as a default constraint, but gives the flexibility of reuse

create default default_name as

constant|expression

• Once a default is created, it can be bound to multiple columns using sp_bindefault

Defaults

create default D_city as 'Chicago'

exec sp_bindefault D_city,authors.city

exec sp_bindefault D_city,employee.city

• To unbind a default, use sp_unbindefault

• To drop a default, use drop default• A default must be unbound from all

columns before it can be dropped

Rule

• A rule is the same as a check constraint, except it exists as an independent object

• Just like a default object, this gives the flexibility to use the rule in many places

• The name of the varibale used inside a rule is arbitrary and can not be directly accessed

create rule rule_name as

conditional_expression

create rule R_state as

@state in ('IL', 'MI', 'MA')

create rule R_salary as

@salary < 1000000

Rule

create rule R_state as @state in ('IL', 'MI', 'MA')

exec sp_bindrule R_state,authors.state

exec sp_bindrule R_state,employee.state

• To unbind a rule, use sp_unbindrule• To drop a rule, use drop rule• A rule must be unbound from all

columns before it can be dropped• Only one rule can be active on a

column at a time• The last rule bound to a column is

the one in effect• If the column also has a check

constriant, then the only acceptable values are those that match both

User Datatypes

• The true power of rules, defaults, and user datatypes comes when they are combined.

• A rule and a default can be bound directly to a user datatype.

• Since the datatype can be used in many columns, this allows you to enforce a rule or default from a single location with a single command

• Any changes to the rule or default are automatically reflected in all columns where that datatype is used

• A rule or default bound directly to a column override the rule or default bound to a column

Precedence

• During an insert, a default is checked first and then any rule

• During an update, the rule is checked first

• A rule or default bound directly to a column overrides the rule or default bound to the user datatype

• The last rule or default bound is the only one that is effective

• If a rule is bound to a column that has a check constraint, the only allowed values are those that meet both the rule and constraint

Definitions

• Just like every other object in the database, information concerning a rule or default can be obtained from the system procedure sp_helptext

sp_helptext object_name

Unique Index

• Unique indexes are used to enforce uniqueness within a column or group of columns

• A unique index is created in three cases:– Primary key constraint is defined– Unique constraint is defined– A unique index is explicitly created

• When the index is created, the data is checked for uniqueness. If duplicates are present, the creation of the index fails

• The index is then enforced on all subsequent inserts and updates

Implementing RI

• Which method to choose?

Unit 8 Review

• Defaults can be created as separate objects

• sp_bindefault binds a default to a column or datatype

• Rules can also be created as separate objects

• sp_bindrule binds a rule to a column or datatype

• Rules and defaults promote reusablity

• They can be combined with user datatypes for increased power and flexibility

• The last rule or default bound to a datatype takes effect

• A rule or default bound directly to a column overrides a rule or default bound to the column's datatype

• A unique index is used to enforce uniqueness within a column or group of columns

Unit 8 Exercises

• Time allotted for exercises is 30 minutes