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Merge pull request #24971 from taosdata/54liuyao-patch-2 

Update 14-stream.md
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@ -41,16 +41,28 @@ window_clause: {
SESSION(ts_col, tol_val)
| STATE_WINDOW(col)
| INTERVAL(interval_val [, interval_offset]) [SLIDING (sliding_val)]
| EVENT_WINDOW START WITH start_trigger_condition END WITH end_trigger_condition
| COUNT_WINDOW(count_val[, sliding_val])
}
```
`SESSION` indicates a session window, and `tol_val` indicates the maximum range of the time interval. If the time interval between two continuous rows are within the time interval specified by `tol_val` they belong to the same session window; otherwise a new session window is started automatically.
`EVENT_WINDOW` is determined according to the window start condition and the window close condition. The window is started when `start_trigger_condition` is evaluated to true, the window is closed when `end_trigger_condition` is evaluated to true. `start_trigger_condition` and `end_trigger_condition` can be any conditional expressions supported by TDengine and can include multiple columns.
`COUNT_WINDOW` is a counting window that is divided by a fixed number of data rows.`count_val`: A constant, which is a positive integer and must be greater than or equal to 2. The maximum value is 2147483648. `count_val` represents the maximum number of data rows contained in each `COUNT_WINDOW`. When the total number of data rows cannot be divided by `count_val`, the number of rows in the last window will be less than `count_val`. `sliding_val`: is a constant that represents the number of window slides, similar to `SLIDING` in `INTERVAL`.
For example, the following SQL statement creates a stream and automatically creates a supertable named `avg_vol`. The stream has a 1 minute time window that slides forward in 30 second intervals to calculate the average voltage of the meters supertable.
```sql
CREATE STREAM avg_vol_s INTO avg_vol AS
SELECT _wstart, count(*), avg(voltage) FROM meters PARTITION BY tbname INTERVAL(1m) SLIDING(30s);
CREATE STREAM streams0 INTO streamt0 AS
SELECT _wstart, count(*), avg(voltage) from meters PARTITION BY tbname EVENT_WINDOW START WITH voltage < 0 END WITH voltage > 9;
CREATE STREAM streams1 IGNORE EXPIRED 1 WATERMARK 100s INTO streamt1 AS
SELECT _wstart, count(*), avg(voltage) from meters PARTITION BY tbname COUNT_WINDOW(10);
```
## Partitions of Stream