Use LEFT and RIGHT arrow keys to navigate between flashcards;
Use UP and DOWN arrow keys to flip the card;
H to show hint;
A reads text to speech;
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
|
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 |