-
What is a column domain?
Its range of permissible values. Eg. for gpa, the range is [0,4).
-
What is a key?
A key consists of one or more attributes that determine other attributes. For example, an invoice no. determines all the invoice attributes like invoice date and customer name.
-
What is an entity?
Person, place, thing, or event about which data will be collected and stored.
-
What is an attribute?
Characteristic of an entity.
-
What is determination?
Is the state in which knowing the value of one attribute makes it possible to determine the value of another.
-
What is dependence?
The value of one or more attributes is dependent upon the values of one or more other attributes. For example a student's last name may be determined by the student no.
-
What is a superkey?
It can uniquely identify any row in the table or functionally determine every attribute in the row.
-
What is entity integrity?
Is the condition in which each row in the table has its own unique identity.
-
How do you ensure entity integrity?
- a) All the values in the primary key must be unique.
- b)No key attribute in the primary key can contain a null.
-
What is a foreign key?
The primary key of one table that has been placed into another table to create a common attribute.
-
What is a secondary key?
A key used strictly for data retrieval purposes.
-
SELECT?
Yields all values in rows in a table to satisfy a given condition.
-
PROJECT?
Yields all values for selected attributes or columns.
-
UNION?
Combines all rows from two tables, excluding duplicate rows.
-
INTERSECT?
Yields only rows that appear in both tables.
-
DIFFERENCE?
Yields all rows in one table that are not found in the other table.
-
PRODUCT?
Yields all possible pairs of rows from two tables.
-
JOIN?
Allows information to be combined from two or more tables. It allows the use of independent tables linked by common attributes.
|
|