A
Aggregate Subquery
A Nested Query that contains an aggregation function in its select list.
Aligned Row Format
A system in which data fields are aligned on 8‑byte boundaries. If a field does not align naturally on an 8-byte boundary, Teradata Database expanded with pad bytes to achieve proper alignment.
Because pad bytes consume extra disk space and result in extra I/O operations, which can impact performance, the Packed64 Row Format is generally preferred to Aligned Row Format.
AMP
Access Module Processor.
Anchor Period Expansion
An expansion based on user‑specified anchored temporal epochs in a time line.
You must specify the SQL keyword PERIOD in the EXPAND ON clause specification to perform anchor period expansions.
Anchor period expansions produce rows whose associated period beginning bounds are aligned to specific DateTime values derived from the anchor names and whose periods overlap the input period being expanded.
Compare with Anchor Point Expansion and Interval Expansion.
Anchor Point Expansion
An expansion based on user‑specified anchored temporal points in a time line.
You must not specify the SQL keyword PERIOD in the EXPAND ON clause specification to perform anchor point expansions.
Anchor point expansions produce rows in a specific date or time anchor point associated with the expanded rows where the points are the anchor points specified for the input period being expanded.
Compare with Anchor Period Expansion and Interval Expansion.
API
Application Programming Interface.
A set of software services with a well‑defined program interface.
B
BLOB
Binary Large OBject.
A data object, usually larger than 64K, that contains only binary data such as pictures, movies, or music.
Compare with CLOB.
BTEQ
Basic Teradata Query facility.
BTET
An option for the Preprocessor2 TRANSACT and -tr commands signifying that the transaction protocol the application is to use is Teradata session mode. For details, see Teradata Preprocessor2 for Embedded SQL Programmer Guide.
The option name is derived from an abbreviation for BT/ET, or BEGIN TRANSACTION/END TRANSACTION, the SQL statements that must delimit all explicit transactions in Teradata session mode. For details, see SQL Request and Transaction Processing.
BYNET
BanYan NETwork, the high speed bus used to link the nodes of a Teradata multiple parallel processing database server.
C
Character String Literal
See String Literal.
CJK
Chinese, Japanese, and Korean.
CLIv2
Call Level Interface Version 2
See Teradata Call-Level Interface Version 2 Reference for Mainframe-Attached Systems or Teradata Call-Level Interface Version 2 Reference for Workstation-Attached Systems for details.
CLOB
Character Large OBject.
A data object, usually larger than 64K, that contains only character data such as XML or other text files.
Compare with BLOB.
Column‑Level Security
A method of controlling access to the columns of a table. Column‑level security is a form of discretionary access control. Another method of access control is row-level security (see Row‑Level Security).
Teradata Database supports column‑level security for the following privileges.
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Constant Expression
An SQL expression that does not make any column references.
Containing Query
See Outer Query.
Correlated Query
A SELECT request that contains a Correlated Subquery.
Correlated Subquery
A Nested Query that contains a predicate that references the relation in its Outer Query.
Correlation Name
An aliased name assigned to a table or view name that is specified in an SQL request. Correlation names are also sometimes called range variables.
Correlation names are associated with a table or view only within the context in which they are defined. Once you specify a correlation name for a table or view name, you must specify that correlation name in any qualified reference to a column of that instance of the table or view instead of specifying the actual table or view name.
CRM
Customer Relationship Management.
D
DB2
DataBase 2.
The general name used for all IBM relational database management system products, though the versions for various platforms do not share a common code base.
DBQL
Database Query Logging.
Derived Table
A derived table is a transitory table that is created dynamically from one or more other tables by evaluating a query expression or table expression. The semantics of derived tables are identical to the semantics of views.
Derived tables must always be defined with a correlation name.
E
E2I
External-to-Internal.
Expand
A SELECT operation that produces one value-equivalent row for each time granule in a time period. The resulting row is time stamped with a single timestamp. Also see Temporal Table Support for details.
F
FIFO
First In, First Out.
A description of a particular type of queue.
FK
Foreign Key.
H
Hash Index
A vertical partition of a base table properties similar to a single‑table Join Index.
Unlike the primary index, hash indexes are stored in separate subtables that must be maintained by the system. Hash index subtables consume disk space, so you should monitor your queries periodically using EXPLAIN modifiers to determine whether the Optimizer is using the hash indexes you designed for your queries. If not, you should drop those indexes or rewrite your queries so that the Optimizer uses them.
HI
I
I2E
Internal-to-External.
IBM
International Business Machines Corporation.
IFP
Interface processor, indicates parsing engine (PE) in diagnostics.
Interval Expansion
An expansion based on one or more user‑specified interval literals such as INTERVAL ‘1’ DAY or INTERVAL ‘3’ MONTH.
You must specify an interval literal in the EXPAND ON clause to invoke an interval expansion. See “EXPAND ON Clause” on page 168.
You cannot specify a BY expansion_interval clause to perform an interval expansion.
An example verbal query that could be formalized using such an expansion is “Compute the moving window average of inventory cost by week during the year 2011."
Compare with Anchor Period Expansion and Anchor Point Expansion.
Irregular Time Series
A sequence of data points measured at asymmetric intervals of a predefined time interval.
Also see Time Series. Compare with Regular Time Series.
J
JI
JIS
Japanese Industrial Standards, an organization that specifies the standards used for industrial activities in Japan.
Join Index
A vertical partition of one or more base tables that can, depending on how it is defined, create various types of prejoins of tables, including sparse and aggregate forms. Join indexes cannot be queried directly by an SQL request. They are used by the Optimizer to enhance the performance of any queries they cover.
A join index that only vertically partitions a base table is referred to as a single‑table join index. A join index that prejoins two or more base tables is referred to as a multitable join index.
Both types of join index can be created in sparse or aggregate forms and can have a subset of their columns compressed.
Unlike the primary index, which is stored in‑line with the row it indexes, join indexes are stored in separate subtables that must be maintained by the system. Join index subtables also consume disk space, so you should monitor your queries periodically using EXPLAIN modifiers to determine whether the Optimizer is using any of the join indexes you designed for them. If not, you should either drop those indexes or rewrite your queries in such a way that the Optimizer does use them.
L
LOB
Large OBject.
Any data object that is larger than the maximum row size for Teradata Database. There are two types of LOB: the BLOB and the CLOB.
Local Subquery
A subquery that does not refer to any columns selecting in an outer query. Local subquery is a synonym for the term Self‑Contained Subquery, and it always refers to noncorrelated subqueries.
LT/ST
Large Table/Small Table (join).
M
Mandatory Access Control
A type of access control in which the database management system constrains the ability of a user to access or perform certain operations on database objects.
The Teradata Database implementation of mandatory access control is referred to as row-level security (see Row‑Level Security).
N
Nested Query
A SELECT request that is contained within another SELECT request.
Depending on which clause of a SELECT request contains the nested query, it has a different name.
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IF the embedded query is specified in this clause … |
THEN it is referred to as a … |
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select list |
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Also see Outer Query, Aggregate Subquery, Nonaggregate Subquery, and Correlated Subquery.
Nonaggregate Subquery
A Nested Query that does not contain an aggregate function in its select list. A nonaggregate subquery can be linked to its Outer Query by means of one of the following SQL operators:
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For information about these operators, see SQL Functions, Operators, Expressions, and Predicates.
NoPI
No Primary Index.
NoPI Table
A table that does not have a primary index or a primary AMP index.
Null
A construct used to represent missing information. Nulls are not values, so the term null value is incorrect usage. The truth value of nulls is usually, but not always, UNKNOWN. For a list of exceptions, see Database Design.
NUPI
NonUnique Primary Index.
NUSI
NonUnique Secondary Index.
O
Object‑Level Security
A method of controlling access to a database object such as a database, table, or view.
OLTP
OnLine Transaction Processing.
Outer Expression
An expression specified in an Outer Query.
Outer Query
A SELECT request that contains a Nested Query is referred to as the outer query in that relationship, while the nested query in the relationship is referred to as the inner query. An outer query is sometimes referred to as a Containing Query.
Outer Reference
A reference to variables in an outer expression by a variable in an inner expression.
P
Packed64 Row Format
A system in which data fields need not be aligned on 8‑byte boundaries, but are instead is stored without pad bytes or other alignment details.
PDE
Parallel Database Extensions. The Teradata virtual machine that permits the database and file system software to communicate with the underlying operating system.
PE
Parsing Engine.
PK
Predicate
A truth‑valued function that describes either a property of objects or a relationship among objects as represented by a set of variables. In relational database management systems, predicates are also referred to as conditions, search conditions, or terms.
The purpose of predicates in SQL queries is to enhance selectivity, narrowing the results set for a query to only those rows that are relevant to the desired outcome.
In the SQL language, predicates are the specifications made in the WHERE clause of any query (including those specified with AND or OR operators), the ON clause of a join or MERGE request specification, the clause of an aggregation, or the QUALIFY clause of an ordered analytic function.
Internally, query optimizers often add predicates to queries in order to create optimization opportunities that would otherwise not be available. This application is derived from work done in the fields of logic and constraint databases.
Primary Condition
In a MERGE request ON clause, the primary condition is the condition that specifies an equality constraint of the primary index of the target table and one of the following source table column elements:
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If there is a Secondary Condition in the ON clause, the primary condition must be conjunctive (ANDed) with it.
Primary Key
A set of columns in a table whose values make each row in that table unique.
Primary keys are a logical, not physical, concept that are often, but not necessarily, used as the primary index for a table when it is physically designed.
A table can have multiple candidate keys, but only one primary key can be defined for it. Those candidate keys that are not used as the primary key for a table are referred to as alternate keys.
Relationships between primary and foreign keys are often used to establish referential integrity between tables. These relationships are also frequently exploited by the Optimizer to enhance query performance.
Q
QITS
Query Insertion TimeStamp.
The first column of any queue table must be a QITS column. See “CREATE TABLE (Queue Table Form)” in SQL Data Definition Language for details.
R
RDBMS
Relational DataBase Management System.
Regular Time Series
A sequence of data points measured at symmetric granules of a predefined time interval.
Also see Time Series. Compare with Irregular Time Series.
Row‑Level Security
A method of controlling access to the rows of a table made possible by the Teradata Row Level Security feature.
For more information on row-level security, see:
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RU
Read Uncommitted.
S
Scalar Subquery
A subquery that can be specified wherever a value expression can be specified. There are two types of scalar subquery: correlated and noncorrelated.
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Secondary Condition
In a MERGE request ON clause, a secondary condition is any condition that is not the Primary Condition.
The elements of a secondary condition in the ON clause can be either conjunctive (ANDed) or disjunctive (ORed) with one another within the secondary condition, but the complete secondary condition term must be ANDed with the primary condition.
Secondary Index
A vertically partitioned subset of base table columns used to facilitate data manipulation operations. The two types of secondary indexes are USI and NUSI.
Unlike the primary index, which is stored in‑line with the row it indexes, secondary indexes are stored in separate subtables that must be maintained by the system. Because secondary index subtables consume disk space, periodic monitoring of your queries using EXPLAIN modifiers can be done to determine whether the Optimizer uses the secondary indexes you designed for your queries. If it is not, you can drop the indexes or rewrite your queries so that the Optimizer uses the indexes.
Teradata does not define the term secondary index in the same way it is commonly used to describe a nonclustered index in an indexing system based on B+ trees.
Security Policy
An element of row-level security (see Row‑Level Security) that defines the SQL actions that can be executed on a row and the privileges required by a user to execute the permitted SQL actions. In Teradata Database, the mechanism used to define and enforce a row-level security policy is a constraint UDF.
Select List
The list of columns, expressions, or both to be projected from a set of tables, views, or both in a SELECT request or Subquery.
Self‑Contained Subquery
A subquery that does not refer to any columns selecting in an outer query. Self‑contained subquery is a synonym for the term Local Subquery, and it always refers to noncorrelated subqueries.
Serializable
Concurrent database transactions are serializable if the system is able to execute the transactions and preserve the integrity of the database. Serializability is an aspect or property of concurrency control. See SQL Request and Transaction Processing for details.
SR
String Literal
Zero or more alphanumeric characters enclosed by APOSTROPHE characters.
Subquery
A SELECT … FROM … WHERE expression that is nested within one or more other SELECT … FROM … WHERE expressions. Also referred to as a Nested Query.
T
TDWM
Teradata Workload Management.
Teradata Row Level Security
A feature of Teradata Database that enables administrators to define and enforce a Security Policy that articulates which users can access particular rows of a table and the actions that can be executed on the rows. The main mechanism used to define and enforce the Security Policy are constraint UDFs. This feature is Teradata’s implementation of Mandatory Access Control.
For more information this feature, see:
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Time Series
An ordered sequence of observations of a variable that are arranged according to the time of their occurrence. Time series are typically measured at some constant frequency and generally, but not necessarily, their data points are spaced at uniform time intervals.
Time series are usually examined using either frequency domain analyses (such as spectral and wavelet analyses) or time domain analyses (such as autocorrelation and crosscorrelation analyses). The time series analyzed using the SQL EXPAND ON clause fall into the category of time domain analysis.
Also see Irregular Time Series and Regular Time Series.
TLE
Target Level Emulation.
A set of tools used to emulate the characteristics of a production environment on a smaller, differently configured test system. See Teradata System Emulation Tool User Guide and SQL Request and Transaction Processing for more information.
U
UCS-2
Universal Coded Character Set containing 2 bytes.
UDT expression
Any expression that returns a UDT result.
Unique Constraint
A constraint that ensures that all values in the column on which it is defined are unique. Examples include unique primary indexes, primary keys, unique secondary indexes, and UNIQUE constraints.
UPI
Unique Primary Index.
USI
Unique Secondary Index.
A Secondary Index designed to facilitate single‑row access.
V - W
vproc
Virtual PROCess.
WAL
Write Ahead Log or Write Ahead Logging.
A transaction logging scheme maintained by the File System in which a write cache for disk writes of permanent data is maintained using log records instead of writing the actual data blocks at the time a transaction is processed. Multiple log records representing transaction updates can then be batched together and written to disk with a single I/O, thus achieving a large savings in I/O operations and enhancing system performance as a result.