Chapter5

equijoin

two join field values were identical

A natural join

also produces the same output but uses a "USING" keyword in the joining clause.

alternate key

alternate key is used to describe a candidate key that was not chosen to be the primary key of the relation

integrating data

would require extracting data from one file and using that extracted data as a search argument to find the sought-after data in the other file.

candidate key

a column, or set of columns, in a table that can uniquely identify any database record without referring to any other data. Each table may have one or more candidate keys, but one candidate key is special, and it is called the primary key

cell

a row/column position

data retrieval

commands and/or process that are ran against the database's relations, and return the desired data.

Relational Database

data in tables where each row in the table holds the same sort of information. In the early 1970s, Ted Codd, an IBM researcher devised 12 laws of normalization. These apply to how the data is stored and relations between different tables.

unique attributes

ensures that the specified attributes always have unique values within a director

attribute

field

column

in a file is referred to as a field

tuple

in a relation, each row as this

foreign key

is a column or group of columns in a relational database table that provides a link between data in two tables. It acts as a cross-reference between tables because it references the primary key of another table, thereby establishing a link between them.

data redundancy

is a condition created within a database or data storage technology in which the same piece of data is held in two separate places.

primary key

is a special relational database table column (or combination of columns) designated to uniquely identify all table records. It's main features are: It must contain a unique value for each row of data. It cannot contain null values. It is either an existing table column or a column that is specifically generated by the database according to a defined sequence.

join operation

is an SQL operation performed to establish a connection between two or more database tables based on matching columns, thereby creating a relationship between the tables.

Relational algebra

is an informal, hypothetical command style for now, there are two commands called Select and Project that are capable of the kinds of horizontal and vertical manipulations just suggested.

Row

record

Relation

tables

domain values

that is, they must both have values of the same type

Relational Database Model

the most common model in industry today. It is based on the relational model developed by E.F. Codd. It allows the definition of data structures, storage and retrieval operations and integrity constraints. In such a database the data and relations between them are organized into tables