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Oracle® Database Lite SQL Reference Release 10.3 Part Number E12092-02 |
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# Glossary

base table

A source of data, either a table or a view, that underlies a view. When you access data in a view, you are really accessing data from its base tables. You specify a view's base tables in CREATE VIEW.

database object

A database object is a named database structure: a table, view, sequence, index, snapshot, or synonym.

foreign key

A foreign key is a column or group of columns in one table or view whose values provide a reference to the rows in another table or view. A foreign key generally contains a value that matches a primary key value in another table.

index

An index is a database object that provides fast access to individual rows in a table. You create an index to accelerate the queries and sorting operations performed against the table's data. You also use indexes to enforce certain constraints on tables, such as unique and primary key constraints.

Indexes, once created, are automatically maintained and used for data access by the database engine whenever possible.

integrity constraint

An integrity constraint is a rule that restricts the values that can be entered into one or more columns of a table.

join

A relationship established between keys (both primary and foreign) in two different tables or views. Joins are used to link tables that have been normalized to eliminate redundant data in a relational database. A common type of join links the primary key in one table to the foreign key in another table to establish a master-detail relationship. A join corresponds to a WHERE clause condition in a SQL statement.

master-detail relationship

A master-detail relationship exists between tables or views in a database when multiple rows in one table or view (the detail table or view) are associated with a single master row in another table or view (the master table or view).

Master and detail rows are normally joined by a primary key column in the master table or view that matches a foreign key column in the detail table or view.

When you change values for the primary key, the application should query a new set of detail records, so that values in the foreign key match values in the primary key. For example, if detail records in the EMP table are to be kept synchronized with master records in the DEPT table, the primary key in DEPT should be DEPTNO, and the foreign key in EMP should be DEPTNO.

positioned DELETE

A positioned DELETE statement deletes the current row of the cursor. Its format is:

    DELETE FROM table
       WHERE CURRENT OF cursor_name

positioned UPDATE

A positioned UPDATE statement updates the current row of the cursor. Its format is:

    UPDATE table SET set_list
       WHERE CURRENT OF cursor_name

primary key

A table's primary key is a column or group of columns used to uniquely identify each row in the table. The primary key provides fast access to the table's records, and is frequently used as the basis of a join between two tables or views. Only one primary key may be defined for each table.

To satisfy a PRIMARY KEY constraint, no primary key value can appear in more than one row of the table, and no column that is part of the primary key can contain a NULL value.

referential integrity

Referential integrity is defined as the accuracy of links between tables in a master-detail relationship that is maintained when records are added, modified, or deleted.

Carefully defined master-detail relationships promote referential integrity. Constraints in your database enforce referential integrity at the database (the server in a client/server environment).

The goal of referential integrity is to prevent the creation of an orphan record, which is a detail record that has no valid link to a master record. Rules that enforce referential integrity prevent the deletion or update of a master record, or the insertion or update of a detail record, that creates an orphan record.

schema

A schema is a named collection of database objects, including tables, views, indexes, and sequences.

sequence

A sequence is a database object that generates a series of unique integers. Sequences are typically used to generate data values that are required to be unique, such as primary key values.

SQL

SQL, or Structured Query Language, is a non-procedural database access language used by most relational database engines. Statements in SQL describe operations to be performed on sets of data. When a SQL statement is sent to a database, the database engine automatically generates a procedure to perform the specified tasks.

synonym

A synonym is an alternative name, or alias, for a table, view, sequence, snapshot, or another synonym.

table

A table is a database object that stores data that is organized into rows and columns. In a well designed database, each table stores information about a single topic (such as company employees or customer addresses).

transaction

A set of changes made to selected data in a relational database. Transactions are usually executed with a SQL statement such as ADD, UPDATE, or DELETE. A transaction is complete when it is either committed (the changes are made permanent) or rolled back (the changes are discarded).

A transaction is frequently preceded by a query, which selects specific records from the database that you want to change.

unique key

A table's unique key is a column or group of columns that are unique in each row of a table. To satisfy a UNIQUE KEY constraint, no unique key value can appear in more than one row of the table. However, unlike the PRIMARY KEY constraint, a unique key made up of a single column can contain NULL values.

view

A view is a customized presentation of data selected from one or more tables (or other views). A view is like a "virtual table" that enables you to relate and combine data from multiple tables (called base tables) and views. A view is a kind of "stored query" because you can specify selection criteria for the data that the view displays.

Views, like tables, are organized into rows and columns. However, views contain no data themselves. Views allow you to treat multiple tables or views as one database object.