Active set The set of rows that satisfy a cursor's query. The active set is assembled when the OPEN CURSOR statement is executed.
Archive logging The process of making a copy of a redo log file when it is completely filled with changed blocks.
Attribute A characteristic or quality associated with an entity. Attributes are defined in a logical data model and implemented as columns.
Auditing The recording of a user's database activity into the AUD$ table. Auditing is controlled with the AUDIT ON statement and enabled by setting the AUDIT_TRAIL initialization parameter to TRUE.
BLOB A binary large object. BLOBs can be stored in a column that is declared as a LONG RAW.
Block The basic building block of an Oracle database. The default size of a block is 2,048 bytes. The block size is determined when the database is created and cannot be changed.
Built-in function One of Oracle's predefined functions that can be referenced in SQL statements.
CLOSE CURSOR The action of closing a cursor and releasing any resources associated with the cursor.
Cluster A group of two or more tables whose rows are stored together based on the common column values by which the tables are related.
Column An attribute or characteristic of the entity on which a table is based.
COMMIT The SQL statement that permanently records row changes to the database file. Once a transaction is committed, all users can see the changes resulting from the transaction.
Concurrency The capability of the Oracle database to support the activity of multiple users. Oracle provides concurrency by enabling one user to view the contents of a table while another user is modifying the contents of the same table.
Constraint A mechanism that ensures that the values of a column or a set of columns satisfy a declared condition.
Control file A small binary file that contains the names of the database files. The control file also maintains a sequence control number that synchronizes the database files.
Correlated subquery A query that is referenced in the WHERE clause of a SELECT statement.
Cost-based optimizer An Oracle software component that uses statistical information about the contents of a table and related indexes to determine the lowest cost plan for retrieving rows for a query.
CURRVAL The current value of a sequence.
Cursor A window into the rows returned by a query.
Data dictionary The set of tables that Oracle uses to maintain information about database objects such as tables, indexes, columns, views, extents, segments, and tablespaces.
Data dictionary table A table used by Oracle to maintain information about its own database objects.
Data dictionary view A view that combines the information from several data dictionary tables to present a comprehensive or consolidated set of information.
Database Expander A Windows-based Database Administration Tool that displays the usage of space in a tablespace and allows a tablespace to be expanded by some increment.
Database file An operating system file whose internal structure is managed by Oracle and in which Oracle objects are stored.
Database link An Oracle object that points to a specific Oracle user in a remote Oracle database.
Database Manager A Windows-based Database Administration Tool that starts up and shuts down an Oracle instance. You can also use Database Manager to change the value of an initialization parameter.
Database shutdown The process of shutting down an Oracle instance in an orderly manner, terminating the Oracle background processes, and releasing other resources such as the System Global Area (SGA).
Database startup The process of starting an Oracle instance by initiating the Oracle background processes and allocating memory for the SGA.
Datafile An operating system file that is dedicated to a tablespace for storing table, index, and cluster data.
DATE An Oracle datatype that stores date and time information in an internal format. A DATE column uses seven bytes of storage. Oracle provides several built-in functions for manipulating and converting DATE columns and expressions. A DATE column contains a value for century, year, month, day, hour, minute, and second.
DECLARE CURSOR The SQL statement that declares a cursor using a SELECT statement. The DECLARE CURSOR statement must be executed before an OPEN CURSOR statement.
DELETE The SQL statement that deletes selected rows from a table based on any specified criteria.
Distributed database A database whose tables are contained in more than one Oracle instance running on separate machines.
Distributed option An optional component of the Oracle RDBMS that supports the use of distributed queries, distributed transactions, snapshots, and replicated tables.
Domain The underlying type associated with an attribute. Many attributes may belong to the same domain. For example, the attributes Distance_Between_Cities and Distance_Traveled could belong to the same domain--;Distance_Km.
Dynamic performance table A table that is created when an Oracle instance is started. Because it is dynamic, this table doesn't use any permanent storage. Dynamic performance tables provide statistics on the current performance of an Oracle instance, such as the names of connected users, values for initialization parameters, and many other measures.
Export A Windows-based Database Administration Tool that copies tables to a proprietary binary file. Export files work in conjunction with the Import tool.
Entity A person, place, thing, or concept that possesses a set of characteristics.
Entity-relationship model A data modeling methodology in which an entity (a relation or table) is related to another entity via a foreign key/primary key relationship.
Exception handler The set of PL/SQL statements that are executed when a specified exception is raised.
Extent A group of contiguous data blocks that are allocated for table, index, or cluster storage.
FETCH The SQL statement that retrieves rows from a cursor's active set.
Foreign key An attribute whose value, if not null, must exist as the primary key value for another entity.
Hash cluster A mechanism for storing table data based on a cluster key value. A hash function is used to quickly access rows whose cluster key is a specified value.
Import A Windows-based Database Administration Tool that reads the contents of an export file. The Import program can load tables and other database objects previously exported with the Export utility.
Index A database object used to improve query performance. An index consists of one or more of a table's columns that are organized as a B*-tree. A unique index is used to enforce a primary key or unique constraint. A nonunique index is only used for performance purposes.
Initialization parameter A parameter whose value is read when an Oracle instance is started. Initialization parameters affect the performance of an Oracle instance and the resources it requires.
INSERT The SQL statement that creates a new row in a table.
INTERSECT The SQL operator that returns the common rows in two sets of rows.
JOIN A query that retrieves column values from more than one table.
Lexicon The pool of legal values associated with a domain. For example, the lexicon for the domain Days_of_the_Week is Sunday through Saturday.
Lock A mechanism that reserves an Oracle resource for the sole use of a transaction or operation. Most locks are automatically issued by the Oracle RDBMS in response to SQL statements. The SELECT FOR UPDATE statement explicitly locks a set of rows.
LONG A column datatype that can store up to 2GB of characters. The following restrictions are imposed on the use of LONG columns: (1) A table can have only one LONG column, and (2) you can't use Oracle's built-in functions with a LONG column.
LONG RAW A column datatype that can store up to 2GB of binary data. The LONG RAW datatype has the same restrictions as the LONG datatype. A LONG RAW column is commonly used for storing BLOBs.
Mandatory column A column for which the NOT NULL constraint is defined. A mandatory column may never have a null value assigned to it.
MINUS The SQL operator that returns the rows that exist in one set of rows but not in a second set of rows.
Mutating table Occurs when a trigger attempts to change the value of a row that already has uncommitted changes.
NEXTVAL A pseudocolumn that is used to retrieve the next value of a sequence.
NULL A keyword that describes a value that is unknown or not applicable.
Object Manager A Windows-based Database Administration Tool used to create and modify tables. Object Manager uses a spreadsheet; each row of the spreadsheet specifies a table's column.
Object privilege The set of privileges that can be granted on a table, view, and other database objects. The object privileges that can be granted to a role or user depend upon the object type. The object privileges for a table are select, insert, update, delete, alter, index, and reference.
OPEN CURSOR The PL/SQL statement that parses the query associated with the cursor and executes it. The qualified rows are referred to as the active set.
Optimizer A component of the Oracle RDBMS that calculates the most efficient execution plan for a query. Oracle has two types of optimizers a rule-based optimizer and a cost-based optimizer.
Oracle instance A set of background processes and SGA executing against a set of Oracle database files.
Outer join A variation of a table join. If the outer join operator is applied to a column, any rows that don't satisfy the join condition are returned with null values.
Package A set of related procedures, functions, and other structures that are stored in an Oracle database. A package consists of an interface specification that is visible to a caller and a package body whose statements are not visible to a caller.
Package body The PL/SQL statements that implement the logic of a package specification.
Parallel query option An Oracle RDBMS option that breaks a query into subtasks, which can be allocated to separate processors.
Parallel server An Oracle RDBMS option that allows multiple Oracle instances to access the same database files.
Password Manager The Personal Oracle utility used to change the database password.
PL/SQL A set of procedural language extensions to the Oracle SQL language. Database triggers, procedures, functions, and packages are written in PL/SQL.
PL/SQL block A PL/SQL program unit consisting of a declaration section, block, and an optional exception section.
Precompiler An Oracle product that enables a developer to embed SQL statements in a third-generation language (3GL) program. An Oracle precompiler for the specific language (for example, COBOL or C) translates the embedded SQL statements into Oracle library calls so that the precompiled program can be compiled and linked into an executable program.
Primary key The set of attributes that uniquely identify a row.
Profile A set of resource limits that can be assigned to a database role or user.
Pseudocolumn A built-in value (or function without arguments) that returns a specific piece of information by querying a table--;usually DUAL. For instance, SYSDATE always returns the current date and time, regardless of the specified table.
Read consistency The Oracle RDBMS will always return data that is consistent within a single statement. For example, suppose a table contains three columns: Product_ID, Quantity_Sold, Quantity_Returned. If you query the table to retrieve Quantity_Sold, Quantity_Returned, and Quantity_Sold + Quantity_Returned, read consistency guarantees that Quantity_Sold + Quantity_Returned is equal to Quantity_Sold added to Quantity_Returned--;for every row.
Read-only transaction A transaction that guarantees read consistency for more than one SQL statement.
Redo log file A file that contains any data blocks that have been modified as a result of database transactions. Every Oracle database has at least two redo log files. Oracle writes to the redo log files in a round-robin fashion.
Relation The theoretical term for a table. A relation consists of attributes (columns) and tuples (rows).
Rollback The act of undoing the changes that have been made by a transaction.
Rollback segment A storage element that contains any table changes made before a transaction is committed.
ROWID A row identifier. Every row has a unique ROWID that corresponds to the block number, file number, and relative row number.
ROWNUM A pseudocolumn that indicates the order of the retrieved row. The ROWNUM for the first returned row is 1. ROWNUM can limit the number of rows that are returned by a query.
Rule-based optimizer The Oracle optimizer that uses the query syntax and the existence of indexes to determine the best execution plan for a query.
Savepoint An interim point in a transaction. A complex transaction may decompose the changes made by the transaction into subtasks. A subtask can be denoted by the declaration of a savepoint. If a subtask is unsuccessful, the transaction can be rolled back to a previous savepoint without losing all of the changes made by the transaction.
Segment The set of extents that have been allocated to a particular Oracle object. Segment types include data, index, cluster, hash, and rollback.
SELECT The SQL statement that retrieves rows from a table or view. The SELECT statement has several clauses that enable the user to specify the query criteria. SELECT statements may also be combined with operators such as INTERSECT, MINUS, and UNION.
SELECT FOR UPDATE The SQL statement that applies a share-row lock on the rows identified by the SELECT statement. SELECT FOR UPDATE prevents two users from changing the same row at the same time.
Sequence A database object that provides a unique, monotonically increasing (or decreasing) number. A sequence is useful for creating customer IDs and other unique identifiers.
Session The activities that are performed by an Oracle user from the time an Oracle connection is established until the user disconnects, or logs off, from the database.
Session Manager A Windows-based Database Administration Tool that displays the names of each Oracle user who is currently connected to an Oracle instance.
SGA See System Global Area.
Shared pool The area of the SGA that contains the data dictionary cache and shared parsed SQL statements.
Snapshot A mechanism in which a local copy of a table is periodically updated from a master table residing in a remote database. A snapshot may be refreshed at a specified interval.
SQLCODE A built-in PL/SQL variable that contains the Oracle error code that resulted from the last executable statement. If SQLCODE is equal to 0, the previous statement was successfully executed.
SQLERRM A built-in PL/SQL variable that contains the error message corresponding to SQLCODE.
SQL*DBA A Windows-based Database Administration Tool that can start up or shut down an Oracle database. All SQL statements can be issued through SQL*DBA. SQL*DBA can also create a new database.
SQL*Loader A Windows-based Database Administration Tool that loads data from flat files into one or more tables. SQL*Loader can load data from fixed- or variable-length records. It can apply SQL functions to modify loaded data or restrict loading to records that satisfy specific criteria.
SQL*Net An Oracle component that allows a client application to establish a remote connection with an Oracle database server. There are two versions of SQL*Net--;version 1 and version 2.
SQL*Plus A Windows-based tool that processes SQL statements interactively. SQL*Plus can process a script containing a set of SQL statements.
Stored function A PL/SQL function that is parsed and stored in the Oracle database. A stored function can be called from a PL/SQL subprogram.
Stored procedure A PL/SQL procedure that is parsed and stored in an Oracle database. A stored procedure can be called from SQL*Plus, a PL/SQL subprogram, and a client application (depending on the client application development tool).
Subquery A SELECT statement that is referenced in an INSERT, UPDATE, or DELETE statement. A SELECT statement may also contain a correlated subquery.
Synonym A pointer to an Oracle user and table or view. A synonym may either be private or public. A private synonym is seen only by its owner. A public synonym is seen by all Oracle users.
SYS user The Oracle account that owns the Oracle data dictionary.
SYSDATE A predefined value or pseudocolumn that always contains the current date and time to the nearest second. SYSDATE can be assigned to any column whose datatype is DATE.
System Global Area The System Global Area (SGA) is a shared memory structure. The SGA includes data block buffers that function as a cache, a shared SQL area for storing parsed SQL statements, and a data dictionary cache.
System privilege A privilege granted to a role or user that gives the grantee the ability to execute a particular SQL statement. An example of a system privilege is the CREATE ANY TABLE privilege, which gives the recipient the ability to create a table.
SYSTEM user An Oracle account that owns tables and other database objects used by Oracle application development tools such as forms and reports. Unlike the SYS user, the SYSTEM user doesn't own any data dictionary tables.
Table The fundamental element of a relational database. Every table has a name and set of one or more columns. Each column has a name and datatype. Once a table has been created, rows may be inserted into it.
Tablespace A logical construct that consists of one or more operating system files referred to as datafiles. When a table, index, cluster, or rollback segment is created, its storage is assigned to a tablespace.
TKPROF An Oracle utility program that interprets trace files to produce a list of the SQL statements and related statistics that were processed during an Oracle session.
Transaction A set of database changes that represent some external event. A transaction consists of those changes that have been made either since the beginning of an Oracle session or since the last COMMIT statement or ROLLBACK statement was issued.
Trigger A PL/SQL block that executes when a SQL statement--;INSERT, UPDATE, or DELETE--;is executed against a table.
TRUNCATE An Oracle SQL statement that deletes the entire contents of a table. Because it doesn't write any changes to a rollback segment, the TRUNCATE TABLE statement cannot be rolled back.
Two-phase commit The mechanism for performing distributed transactions in which the transaction is committed in two phases. Each node commits its changes. If each node acknowledges that its commit is successful, the distributed transaction is committed on all nodes.
UNION The SQL operator that returns the distinct rows from two or more sets of rows.
UNION ALL The SQL operator that returns the rows, including duplicates, from two or more sets of rows.
UPDATE The SQL statement that modifies the column values of a set of rows in a table based on specified criteria.
User Manager A Windows-based Database Administration Tool that creates a new Oracle user, alters an existing user by granting or revoking roles to that user, and drops an existing user.
VARCHAR2 An Oracle datatype that stores character data. A column defined as VARCHAR2 may store up to 2,000 characters.
View A stored query or virtual table that is based upon one
or more base tables.