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15 Cards in this Set

  • Front
  • Back
Entity Integrity

Condition in which each row in the table has its own unique identity.


-Every table must have a primary key.


-A primary key cannot be NULL.




Purpose - Each row will have a unique identity, and foreign key values can properly reference primary key values.

Referential Integrity

Mechanism the system provides to maintain foreign keys.


- A foreign key must have matching values in the primary key of another table.




Purpose: It is possible for an attribute not to have corresponding value but it is impossible to have an invalid entry. It is impossible to delete a row in a table whose primary keys has mandatory matching foreign key values in another table.



Primary Key
A primary key is a table column that can be used to uniquely identify every row of the table. Any column that has this property will do -- these columns are called candidate keys. A table can have many candidate keys but only one primary key. The primary key cannot be null.


Composite Key

A composite primary key is a primary key consisting of more than one column.

Foreign Key
A foreign key is a column, or combination of columns, that contain values that are found in the primary key of some table (including, possibly, itself). A foreign key may be null, and almost always is not unique.
Super Key
An attribute or combination of attributes that uniquely identifies each row in a table.
Candidate Key
A minimal (irreducible) superkey; a superkey that does not contain a subset of attributes that is itself a superkey.
Secondary Key
An attribute or combination of attributes used strictly for data retrieval purposes.
SQL Stuff (Relational Ops)

Select - is used to select data from a DB.


Project - Selecting the values of a few attributes, rather than selecting all attributes of the Table.


Union - The UNION operator is used to combine the result-set of two or more SELECT statements.


Intersect - is a query that allows you to select related information from 2 tables, this is combine 2 SELECT statement into 1 and display it out.


Difference - (MORE TO BE ADDED LATER)

Inner Join

Returns matched records from the tables that are being joined.




Natural Join - Links tables by selecting only the rows with common values in their common attributes.




Equijoin - Links tables on the basis of an equality condition that compares specified columns of each table.

Outer Join


Matched pairs are retained and unmatched values in the other table are left null.




Left Outer Join - Yields all of the rows in the first table, including those that don't have a matching value in the second table.




Right Outer Join - Yields all of the rows in the second table, including those that do not have matching values in the first table.

Data Dictionary

Description of all tables in the database created by the user and designer. "The DB designers DB" it records the design decisions about tables and their structures.
Relational DB MODELS

 

Relational database model enables logical representation of the data and its relationships

Logical simplicity yields simple and effective database design methodologies

Facilitated by the creation of data relationships based on a logical construct called a relation

Functional Dependence

 

Functional dependence: Value of one or more attributes determines the value of one or more other attributes

Determinant: Attribute whose value determines another

Dependent: Attribute whose value is determined by the other attribute


Full Functional Dependence

 



Full functional dependence: Entire collection of attributes in the determinant is necessary for the relationship