externaldata operator

The externaldata operator returns a table whose schema is defined in the query itself, and whose data is read from an external storage artifact, such as a blob in Azure Blob Storage.


externaldata ( ColumnName : ColumnType [, ...] ) [ StorageConnectionString ] [with ( Prop1 = Value1 [, ...] )]


  • ColumnName, ColumnType: The arguments define the schema of the table. The syntax is the same as the syntax used when defining a table in .create table.

  • StorageConnectionString: The storage connection string describes the storage artifact holding the data to return.

  • Prop1, Value1, ...: Additional properties that describe how to interpret the data retrieved from storage, as listed under ingestion properties.

    • Currently supported properties: format and ignoreFirstRecord.
    • Supported data formats: Any of the ingestion data formats are supported, including CSV, TSV, JSON, Parquet, Avro.


This operator does not have a pipeline input.


The externaldata operator returns a data table of the given schema whose data was parsed from the specified storage artifact, indicated by the storage connection string.


The following example shows how to find all records in a table whose UserID column falls into a known set of IDs, held (one per line) in an external blob. Because the set is indirectly referenced by the query, it can be large.

| where UserID in ((externaldata (UserID:string) [
      h@"?...SAS..." // Secret token needed to access the blob
| ...

The following example queries multiple data files stored in external storage.

externaldata(Timestamp:datetime, ProductId:string, ProductDescription:string)
| summarize count() by ProductId

The above example can be thought of as a quick way to query multiple data files without defining an external table.


Data partitioning isn't recognized by the externaldata() operator.