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isnull()

Applies to: ✅ Microsoft Fabric ✅ Azure Data Explorer ✅ Azure Monitor ✅ Microsoft Sentinel

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

Note

String values can't be null. Use isempty to determine if a value of type string is empty or not.

Syntax

isnull(Expr)

Learn more about syntax conventions.

Parameters

Name Type Required Description
Expr scalar ✔️ 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):

x isnull(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.

Run the query

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

Output

StartTime EndTime EpisodeId EventId State EventType BeginLat BeginLon
2007-01-01T00:00:00Z 2007-01-01T05:00:00Z 4171 23358 WISCONSIN Winter Storm
2007-01-01T00:00:00Z 2007-01-31T23:59:00Z 1492 7067 MINNESOTA Drought
2007-01-01T00:00:00Z 2007-01-31T23:59:00Z 1492 7068 MINNESOTA Drought
2007-01-01T00:00:00Z 2007-01-31T23:59:00Z 1492 7069 MINNESOTA Drought
2007-01-01T00:00:00Z 2007-01-31T23:59:00Z 1492 7065 MINNESOTA Drought
2007-01-01T00:00:00Z 2007-01-31T23:59:00Z 1492 7070 MINNESOTA Drought
2007-01-01T00:00:00Z 2007-01-31T23:59:00Z 1492 7071 MINNESOTA Drought
2007-01-01T00:00:00Z 2007-01-31T23:59:00Z 1492 7072 MINNESOTA Drought
2007-01-01T00:00:00Z 2007-01-31T23:59:00Z 2380 11735 MINNESOTA Drought
2007-01-01T00:00:00Z 2007-01-31T23:59:00Z 1492 7073 MINNESOTA Drought
2007-01-01T00:00:00Z 2007-01-31T23:59:00Z 2240 10857 TEXAS Drought
2007-01-01T00:00:00Z 2007-01-31T23:59:00Z 2240 10858 TEXAS Drought
2007-01-01T00:00:00Z 2007-01-31T23:59:00Z 1492 7066 MINNESOTA Drought
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