row_window_session()

Calculates session start values of a column in a serialized row set.

Syntax

row_window_session ( Expr , MaxDistanceFromFirst , MaxDistanceBetweenNeighbors [, Restart] )

Parameters

Returns

The function returns the values at the beginning of each session. It uses the following conceptual calculation model:

1. Iterates over the input sequence of Expr values in order.

2. For each value, it decides whether to create a new session.

3. If a new session is created, the function returns the current value of Expr. Otherwise, it returns the previous value of Expr.

MaxDistanceFromFirst. plus MaxDistanceBetweenNeighbors.

Examples

The following example calculates session start values for a table, datatable, with a sequence ID column and a Timestamp column to record the time of each record. The data is sorted by the sequence IDs and timestamps and then the example returns values for ID, Timestamp, and a new SessionStarted column. A session can’t exceed one hour. It continues for as long as records are less than five minutes apart and the ID stays the same. The example includes records that are less than five minutes apart.

datatable (ID:string, Timestamp:datetime) [
    "1", datetime(2024-04-11 10:00:00),
    "2", datetime(2024-04-11 10:18:00),
    "1", datetime(2024-04-11 11:00:00),
    "3", datetime(2024-04-11 11:30:00),
    "2", datetime(2024-04-11 13:30:00),
    "2", datetime(2024-04-11 10:16:00)
]
| sort by ID asc, Timestamp asc
| extend SessionStarted = row_window_session(Timestamp, 1h, 5m, ID != prev(ID))

Output

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