17.05 - SELECT and Queue Tables - Advanced SQL Engine - Teradata Database

Teradata Vantage™ - SQL Data Manipulation Language

Product
Advanced SQL Engine
Teradata Database
Release Number
17.05
Release Date
January 2021
Content Type
Programming Reference
Publication ID
B035-1146-175K
Language
English (United States)

A queue table is similar to an ordinary base table, with the additional unique property of being similar to an asynchronous first-in-first-out (FIFO) queue.

The first column of a queue table always contains Queue Insertion TimeStamp (QITS) values. The QITS value of a row indicates the time the row was inserted into the queue table, unless a different, user-supplied value is inserted.

The CREATE TABLE statement for the table must define the first column with the following data type and attributes:

     TIMESTAMP(6) NOT NULL DEFAULT CURRENT_TIMESTAMP(6)

You can use SELECT statements to perform a FIFO peek on a queue table. In this case, data is returned from the queue table without deleting any of its rows.

If no rows are available, no rows are returned. The transaction does not enter a delay state.

To return the queue in FIFO order, specify the first column of the queue table in the ORDER BY clause of the SELECT statement.

To perform a FIFO pop on a queue table, use a SELECT AND CONSUME statement. For more information, see SELECT AND CONSUME.

A SELECT AND CONSUME statement cannot specify a scalar subquery.

For more information about how to define a queue table, see Teradata Vantage™ - SQL Data Definition Language Detailed Topics , B035-1184 .