16.20 - FIRST - Teradata Database - Teradata Vantage NewSQL Engine

Purpose

Returns the oldest value, determined by the timecode, for each group. FIRST is a single-threaded function.

To invoke the FIRST function, use the GROUP BY TIME clause.

Syntax

Syntax Elements

value_expression

A literal or column expression to evaluate.

The value_expression cannot be a reference to a view column derived from a function, and cannot contain any ordered analytical or aggregate functions.

Return Values

The return value is the same data type as the input data type.

Nulls are not included in the result computation.

Usage Notes

FIRST is only valid on numeric data.

In the event of a tie, such as simultaneous timecode values for a particular group, all tied results are returned. If a sequence number is present with the data, it can break a tie, assuming it is unique across identical timecode values.

Example: Using FIRST to Return the Temperature

/*PTI Table*/
SELECT $TD_TIMECODE_RANGE, $TD_GROUP_BY_TIME, BUOYID, FIRST(TEMPERATURE)
FROM OCEAN_BUOYS
WHERE TD_TIMECODE BETWEEN TIMESTAMP '2014-01-06 08:00:00' AND TIMESTAMP '2014-01-06 10:30:00'
GROUP BY TIME (MINUTES(10) AND BUOYID)
ORDER BY 2,3,4;

/*Non-PTI Table*/
SELECT $TD_TIMECODE_RANGE, $TD_GROUP_BY_TIME, BUOYID, FIRST(TEMPERATURE)
FROM OCEAN_BUOYS_NONPTI
WHERE TIMECODE BETWEEN TIMESTAMP '2014-01-06 08:00:00' AND TIMESTAMP '2014-01-06 10:30:00'
GROUP BY TIME (MINUTES(10) AND BUOYID)
USING TIMECODE(TIMECODE)
ORDER BY 2,3,4;

The result set is the same for both examples. The ties are returned in Rows 3 and 4, below.