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Update 14-stream.md

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@ -148,7 +148,7 @@ T = latest event time - watermark
The window closing time for each batch of data that arrives at the system is updated using the preceding formula, and all windows are closed whose closing time is less than T. If the triggering method is WINDOW_CLOSE or MAX_DELAY, the aggregate result for the window is pushed. The window closing time for each batch of data that arrives at the system is updated using the preceding formula, and all windows are closed whose closing time is less than T. If the triggering method is WINDOW_CLOSE or MAX_DELAY, the aggregate result for the window is pushed.
Stream processing strategy for expired data ## Stream processing strategy for expired data
The data in expired windows is tagged as expired. TDengine stream processing provides two methods for handling such data: The data in expired windows is tagged as expired. TDengine stream processing provides two methods for handling such data:
1. Drop the data. This is the default and often only handling method for most stream processing engines. 1. Drop the data. This is the default and often only handling method for most stream processing engines.
@ -157,6 +157,14 @@ The data in expired windows is tagged as expired. TDengine stream processing pro
In both of these methods, configuring the watermark is essential for obtaining accurate results (if expired data is dropped) and avoiding repeated triggers that affect system performance (if expired data is recalculated). In both of these methods, configuring the watermark is essential for obtaining accurate results (if expired data is dropped) and avoiding repeated triggers that affect system performance (if expired data is recalculated).
## Stream processing strategy for modifying data
TDengine provides two ways to handle modified data, which are specified by the IGNORE UPDATE option:
1. Check whether the data has been modified, i.e. IGNORE UPDATE 0, and recalculate the corresponding window if the data has been modified.
2. Do not check whether the data has been modified, and calculate all the data as incremental data, i.e. IGNORE UPDATE 1, the default configuration.
## Supported functions ## Supported functions
All [scalar functions](../function/#scalar-functions) are available in stream processing. All [Aggregate functions](../function/#aggregate-functions) and [Selection functions](../function/#selection-functions) are available in stream processing, except the followings: All [scalar functions](../function/#scalar-functions) are available in stream processing. All [Aggregate functions](../function/#aggregate-functions) and [Selection functions](../function/#selection-functions) are available in stream processing, except the followings: