Integrity Rules

• Integrity rules may sound very technical but they are simple and straightforward rules that each table must follow.
• These are very important in database design, when tables break any of the integrity rules our database will contain errors when retrieving information.
• Hence the name "integrity" which describes reliability and consistency of values.
• there are two types of integrity rules that we will look at:
• Entity Integrity Rule
• Referential Integrity Rule

Entity Integrity Rule: 

• The entity integrity rule refers to rules the primary key must follow. 
• The primary key value cannot be null.
• The primary key value must be unique.
• If a table does not meet these two requirements, we say the table is violating the entity integrity rule.

• The team table violates the entity integrity rules at two places. 
• Team Super- missing primary key
• Super Ultra Mega Team and Best Team in the World -has the same primary key. 

Referential Integrity Rule: 

• The referential integrity rule refers to the foreign key.
• The foreign key may be null and may have the same value but:
• The foreign key value must match a record in the table it is referring to.
• Tables that do not follow this are violating the referential integrity rule.

• The Player table violates the referential integrity rule at these places: 
• Player P8 and P9 - these players are in teamID T8, which does not exist in the Team Table.