Amazon Kinesis Data Analytics
SQL Reference

TOP_K_ITEMS_TUMBLING Function

Returns the most frequently occurring values in the specified in-application stream column over a tumbling window. This can be used to find trending (most popular) values in a specified column.

For example, the Getting Started exercise uses a demo stream that provides continuous stock price updates (ticker_symbol, price, change, and other columns). Suppose you want to find the three most frequently traded stocks in each 1-minute tumbling window. You can use this function to find those ticker symbols.

When you use TOP_K_ITEMS_TUMBLING, be aware of the following:

  • Counting each incoming record on your streaming source is not efficient, therefore the function approximates the most frequently occurring values. For example, when seeking the three most traded stocks, the function may return three of the five most traded stocks.

The function operates on a tumbling window. You specify the window size as a parameter.

For a sample application with step-by-step instructions, see Most Frequently Occurring Values.

Syntax

TOP_K_ITEMS_TUMBLING ( in-application-streamPointer, 'columnName',      K, windowSize, )

Parameters

The following sections describe the parameters.

in-application-streamPointer

Pointer to an in-application stream. You can set a pointer using the CURSOR function. For example, the following statement sets a pointer to InputStream.

CURSOR(SELECT STREAM * FROM InputStream)

columnName

Column name in your in-application stream that you want to use to compute the topK values. Note the following about the column name:

Note

The column name must appear in single quotation marks ('). For example, 'column1'.

K

Using this parameter, you specify how many of the most frequently occurring values from a specific column you want returned. The value K must be greater than or equal to one and cannot exceed 100,000.

windowSize

Size of the tumbling window in seconds. The size must be greater than or equal to one second and must not exceed 3600 seconds (one hour).

Examples

Example Dataset

The examples following are based on the sample stock dataset that is part of Getting Started in the Amazon Kinesis Analytics Developer Guide. To run each example, you need an Amazon Kinesis Analytics application that has the sample stock ticker input stream. To learn how to create an Analytics application and configure the sample stock ticker input stream, see Getting Started in the Amazon Kinesis Analytics Developer Guide.

The sample stock dataset has the schema following.

(ticker_symbol VARCHAR(4), sector VARCHAR(16), change REAL, price REAL)

Example 1: Return the Most Frequently Occurring Values

The following example retrieves the most frequently occuring values in the sample stream created in the Getting Started tutorial.

CREATE OR REPLACE STREAM DESTINATION_SQL_STREAM ( "TICKER_SYMBOL" VARCHAR(4), "MOST_FREQUENT_VALUES" BIGINT ); CREATE OR REPLACE PUMP "STREAM_PUMP" AS INSERT INTO "DESTINATION_SQL_STREAM" SELECT STREAM * FROM TABLE (TOP_K_ITEMS_TUMBLING( CURSOR(SELECT STREAM * FROM "SOURCE_SQL_STREAM_001"), 'TICKER_SYMBOL', -- name of column in single quotes 5, -- number of the most frequently occurring values 60 -- tumbling window size in seconds ) );

The preceding example outputs a stream similar to the following.

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