Data Warehousing

An Index is an optional structure associated with a table to have direct access to rows, which can be created to increase the performance of data retrieval. Index can be created on one or more columns of a table.

An Extent is a specific number of contiguous data blocks, obtained in a single allocation, and used to store a specific type of information.

An integrity constraint is a declarative way to define a business rule for a column of a table.

Clusters are groups of one or more tables physically stores together to share common columns and are often used together.

Each Index has an Index segment that stores all of its data.

Update And Delete Restrict - A referential integrity rule that disallows the update or deletion of referenced data. DELETE Cascade - When a referenced row is deleted all associated dependent rows are deleted.

A table is the basic unit of data storage in an ORACLE database. The tables of a database hold all of the user accessible data. Table data is stored in rows and columns.

A row is stored in a hash cluster based on the result of applying a hash function to the row's cluster key value. All rows with the same hash key value are stores together on disk.

A rule defined on a column (or set of columns) in one table that allows the insert or update of a row only if the value for the column or set of columns (the dependent value) matches a value in a column of a related table (the referenced value). It also specifies the type of data manipulation allowed on referenced data and the action to be performed on dependent data as a result of any action on referenced data.

A Private Synonyms can be accessed only by the owner.

A schema is collection of database objects of a User.

A database link is a named object that describes a "path" from one database to another.

A database is divided into Logical Storage Unit called table spaces. A table space is used to grouped related logical structures together.

A Control file records the physical structure of the database. It contains the following information. Database Names and locations of a database's files and redo log files. And Time stamp of database creation.

A Database contains one or more Rollback Segments to temporarily store "undo" information.

A data block size is specified for each ORACLE database when the database is created. A database users and allocated free database space in ORACLE data blocks. Block size is specified in INIT.ORA file and can't be changed latter.

A data file can be associated with only one database. Once created a data file can't change size. One or more data files form a logical unit of database storage called a table space.

The goal of the optimizer is to choose the most efficient way to execute a SQL statement.

The Optimizer chooses Cost based approach and optimizes with the goal of best throughput if statistics for at least one of the tables accessed by the SQL statement exist in the data dictionary. Otherwise the OPTIMIZER chooses RULE based approach.

A view is a virtual table. Every view has a Query attached to it. (The Query is a SELECT statement that identifies the columns and rows of the table(s) the view uses.)