database

24 cards·by shad

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Raw Facts

data

result of processing raw data to reveal meaning

Information

data about data

Metadata

one or more attributes that determine other attributes

Key

Attribute B functionally dependent on A if all rows in table that agree in value for A also agree in value for B

Functional independence

Key composed of more than one attribute

Composite key

Any key that uniquely identifies each row

Superkey

A superkey without unnecessary attributes

Candidate key

An attribute whose values match primary key values in the related table

Foreign key

FK contains a value that refers to an existing valid tuple (row) in another relation

Referential integrity

Expresses minimum and maximum number of entity occurrences associated with one occurrence of related entity

Cardinality

Process for evaluating and correcting table structures to minimize data redundancies

Normalization

produces a lower normal form

Denormalization

A table is in the First Normal Form When?

All key attributes are defined. There are no repeating groups in the table. All attributes are dependent on primary key. Tabular Format.

Table is in second normal form (2NF) when

It is in 1NF and No attribute is dependent on only portion of primary key.

A table is in third normal form (3NF) when

It is in 2NF and it contains no transitive dependencies

Table is in fourth normal form (4NF) when

It is in 3NF and No multiple sets of multivalued dependencies

What does Show Databases; do?

Show all databases

What does Select do in SQL?

Grabs items in a database.

What is a Lost Update?

Two concurrent transactions update same data element. Overwritten by the other transaction.

Uncommitted data?

Two transactions executed concurrently. First transaction rolled back after second already accessed uncommitted data.

What does a lock do?

Guarantees exclusive use of a data item to a current transaction.

What is Database performance tuning?

Set of activities and procedures designed to reduce response time of database system.

Good database performance starts with?

good database design.