isnull()

Learn how to use the isnull() function to check if the argument value is null.

Evaluates an expression and returns a Boolean result indicating whether the value is null.

Syntax

isnull(Expr)

Parameters

NameTypeRequiredDescription
Exprscalar✔️The expression to evaluate whether the value is null. The expression can be any scalar value other than strings, arrays, or objects that always return false. For more information, see The dynamic data type.

Returns

Returns true if the value is null and false otherwise. Empty strings, arrays, property bags, and objects always return false.

The following table lists return values for different expressions (x):

xisnull(x)
""false
"x"false
parse_json("")true
parse_json("[]")false
parse_json("{}")false

Example

Find the storm events for which there’s no begin location.

StormEvents
| where isnull(BeginLat) and isnull(BeginLon)
| project StartTime, EndTime, EpisodeId, EventId, State, EventType, BeginLat, BeginLon

Output

StartTimeEndTimeEpisodeIdEventIdStateEventTypeBeginLatBeginLon
2007-01-01T00:00:00Z2007-01-01T05:00:00Z417123358WISCONSINWinter Storm
2007-01-01T00:00:00Z2007-01-31T23:59:00Z14927067MINNESOTADrought
2007-01-01T00:00:00Z2007-01-31T23:59:00Z14927068MINNESOTADrought
2007-01-01T00:00:00Z2007-01-31T23:59:00Z14927069MINNESOTADrought
2007-01-01T00:00:00Z2007-01-31T23:59:00Z14927065MINNESOTADrought
2007-01-01T00:00:00Z2007-01-31T23:59:00Z14927070MINNESOTADrought
2007-01-01T00:00:00Z2007-01-31T23:59:00Z14927071MINNESOTADrought
2007-01-01T00:00:00Z2007-01-31T23:59:00Z14927072MINNESOTADrought
2007-01-01T00:00:00Z2007-01-31T23:59:00Z238011735MINNESOTADrought
2007-01-01T00:00:00Z2007-01-31T23:59:00Z14927073MINNESOTADrought
2007-01-01T00:00:00Z2007-01-31T23:59:00Z224010857TEXASDrought
2007-01-01T00:00:00Z2007-01-31T23:59:00Z224010858TEXASDrought
2007-01-01T00:00:00Z2007-01-31T23:59:00Z14927066MINNESOTADrought
……………………