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3.2: Implementing Constraints
70-432
15
Computer Science
Not Applicable
06/16/2010

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Term
What is the purpose of a constraint?
Definition
Enforce business rules and data consistency.
Term
What is a primary key?
Definition
Defines the column(s) that uniquely identify each row of data in the table.
Term
What is the default type of primary key?
Definition
Clustered primary key
Term
Does a primary key affect how data is stored in a table?
Definition
YES.  It stores the data sorted by the primary key.
Term
When is compression applied to the primary key for a table that is compressed?
Definition
When the table is rebuilt.
Term
What is the purpose of a foreign key?
Definition
To implement referential integrity between tables.
Term
Should you use the CASCADE option on a foreign key?
Definition
NO. The cascade option can cause unintended deletions in other tables when that primary key value is deleted. 
It is better to orphan data than delete it.
Term
What are the types of constraints?
Definition
UNIQUE, CHECK, PRIMARY KEY, FOREIGN KEY, NOT NULL
Term
What is the purpose of a UNIQUE constraint?
Definition
Restrict a column to contain unique values in that table.
Term
Can a primary key contain NULLs?  Can a column with a UNIQUE constraint contain NULLs?
Definition
  1. NO. Primary keys cannot have any NULL values. 
  2. NO. Unique constraints can have exactly one NULL in that column.
Term
Under what operations does a DEFAULT constraint apply?
Definition
New rows added under BCP, BULK INSERT, and INSERT
Term
What action does a DEFAULT constraint provide?
Definition
Gives a default value for that column when a value is not otherwise provided.
Term
Can CHECK constraints compare values to values in another column?
Definition
A) YES, for a TABLE-LEVEL CHECK constraint, but only within the same table. 
B) A COLUMN-LEVEL CHECK constraints cannot reference other columns in the table, and the value must fall within a predefined range of values.
Term
What operators can be used for CHECK constraints?
Definition
>, <, =, <=, >=, <>
Term
Can CHECK constraints use wildcards?
Definition
YES. % and _ are allowed.
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