# Document History
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The following table describes important changes to the documentation since the last release of the Amazon Kinesis Data Analytics SQL Reference.
+ **API version: 2015-08-14** 
+ **Latest documentation update:** March 19, 2018


| Change | Description | Date | 
| --- | --- | --- | 
| New HOTSPOTS function | Locate and return information about relatively dense regions in your data. For more information, see [HOTSPOTS](sqlrf-hotspots.md). | March 19, 2018 | 
| Stream-to-stream JOIN examples | Examples for JOIN clause queries. For more information, see [JOIN clause](sql-reference-join-clause.md). | February 28, 2018 | 
| New TSDIFF function | Obtain the difference between two time stamps. For more information, see [TSDIFF](sql-reference-tsdiff.md). | December 11, 2017 | 
| New RANDOM\_CUT\_FOREST\_WITH\_EXPLANATION function | Get an explanation of what fields contribute to an anomaly score in a data stream. For more information, see [RANDOM\_CUT\_FOREST\_WITH\_EXPLANATION](sqlrf-random-cut-forest-with-explanation.md). | November 2, 2017 | 
| New REGEX\_LOG\_PARSE function | Get regex matches from a source string in columnar format. For more information, see [REGEX\_LOG\_PARSE](sql-reference-regex-log-parse.md). | August 21, 2017 | 
| Table of contents reorganization | Topic categories are now more intuitive. | August 18, 2017 | 
| New SQL functions | Addition of [STEP](sql-reference-step.md), [LAG](sql-reference-lag.md), [TO\_TIMESTAMP](sql-reference-to-timestamp.md), [UNIX\_TIMESTAMP](sql-reference-unix-timestamp.md), [REGEX\_REPLACE](sql-reference-regex-replace.md), and addition of regex support to [SUBSTRING](sql-reference-substring.md) | August 3, 2017 | 
| New guide | This is the first release of the Amazon Kinesis Data Analytics SQL Reference guide. | August 11, 2016 |