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.create-or-alter materialized-view

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Applies to: ✅ Microsoft Fabric ✅ Azure Data Explorer

Creates a materialized view or alters an existing materialized view.

Permissions

You must have at least Materialized View Admin permissions to run this command.

Syntax

.create-or-alter materialized-view [ with (PropertyName = PropertyValue,...)] MaterializedViewName on table SourceTableName { Query }

Learn more about syntax conventions.

Parameters

Name Type Required Description
PropertyName, PropertyValue string List of properties in the form of name and value pairs, from the list of supported properties.
MaterializedViewName string ✔️ Name of the materialized view. The view name can't conflict with table or function names in the same database and must adhere to the identifier naming rules.
SourceTableName string ✔️ Name of source table on which the view is defined.
Query string ✔️ Query definition of the materialized view.

Supported properties

New table

If the table is new, the following properties are supported in the with(PropertyName = PropertyValue ). All properties are optional.

Name Type Description
backfill bool Whether to create the view based on all records currently in SourceTable (true), or to create it from now on (false). Default is false. For more information, see Backfill a materialized view.
effectiveDateTime datetime Relevant only when you're using backfill. If it's set, creation backfills only with records ingested after the datetime. backfill must also be set to true. This property expects a datetime literal; for example, effectiveDateTime=datetime(2019-05-01).
updateExtentsCreationTime bool Relevant only when you're using backfill. If it's set to true, Extent Creation time is assigned based on the datetime group-by key during the backfill process. For more information, see Backfill a materialized view.
lookback timespan Valid only for arg_max/arg_min/take_any materialized views. It limits the period of time in which duplicates are expected. For example, if a lookback of 6 hours is specified on an arg_max view, the deduplication between newly ingested records and existing ones will take into consideration only records that were ingested up to 6 hours ago.

Lookback is relative to ingestion_time(). If the materialized view query does not preserve the ingestion_time() value, lookback cannot be defined on the view. See materialized views limitations and known issues. Defining the lookback period incorrectly might lead to duplicates in the materialized view. For example, if a record for a specific key is ingested 10 hours after a record for the same key was ingested, and the lookback is set to 6 hours, that key will be a duplicate in the view. The lookback period is applied during both materialization time and query time.
autoUpdateSchema bool Whether to automatically update the view on source table changes. Default is false. This option is valid only for views of type arg_max(Timestamp, *)/arg_min(Timestamp, *)/take_any(*) (only when the column's argument is *). If this option is set to true, changes to the source table will be automatically reflected in the materialized view.
dimensionTables array A dynamic argument that includes an array of dimension tables in the view. See Query parameter.
folder string The materialized view's folder.
docString string A string that documents the materialized view.
allowMaterializedViewsWithoutRowLevelSecurity bool Allows creating a materialized view over a table with row level security policy enabled.

Existing table

If the table already exists, only the following subset of properties are supported in the with(PropertyName = PropertyValue ). All properties are optional.

Name Type Description
lookback timespan Valid only for arg_max/arg_min/take_any materialized views. It limits the period of time in which duplicates are expected. For example, if a lookback of 6 hours is specified on an arg_max view, the deduplication between newly ingested records and existing ones will take into consideration only records that were ingested up to 6 hours ago.

Lookback is relative to ingestion_time. Defining the lookback period incorrectly might lead to duplicates in the materialized view. For example, if a record for a specific key is ingested 10 hours after a record for the same key was ingested, and the lookback is set to 6 hours, that key will be a duplicate in the view. The lookback period is applied during both materialization time and query time.
autoUpdateSchema bool Whether to automatically update the view on source table changes. Default is false. This option is valid only for views of type arg_max(Timestamp, *)/arg_min(Timestamp, *)/take_any(*) (only when the column's argument is *). If this option is set to true, changes to the source table will be automatically reflected in the materialized view.
dimensionTables array A dynamic argument that includes an array of dimension tables in the view. See Query parameter.
folder string The materialized view's folder.
docString string A string that documents the materialized view.

Returns

Output schema:

Name Type Description
Name string Name of the materialized view.
SourceTable string Name of source table on which the view is defined.
Query string Query definition of the materialized view.
MaterializedTo datetime Maximum materialized ingestion_time() timestamp in source table. For more information, see how materialized views work.
LastRun datetime Last time materialization was run.
LastRunResult string Result of last run. Returns Completed for successful runs, otherwise Failed.
IsHealthy bool true when view is considered healthy, false otherwise. View is considered healthy if it was successfully materialized up to the last hour (MaterializedTo is greater than ago(1h)).
IsEnabled bool true when view is enabled (see Disable or enable materialized view).
Folder string Folder under which the materialized view is created.
DocString string Description assigned to the materialized view.
AutoUpdateSchema bool Whether the view is enabled for auto updates.
EffectiveDateTime datetime Effective date time of the view, determined during creation time (see .create materialized-view).
Lookback timespan Time span limiting the period of time in which duplicates are expected.

Examples

Create or alter a materialized view

The following command creates a new or alters an existing materialized view called ArgMax:

.create-or-alter materialized-view ArgMax on table T
{
    T | summarize arg_max(Timestamp, *) by User
}

Output

Name SourceTable Query MaterializedTo LastRun LastRunResult IsHealthy IsEnabled Folder DocString AutoUpdateSchema EffectiveDateTime Lookback
ArgMax T T | summarize arg_max(Timestamp, *) by User 2023-02-26T16:40:03.3345704Z 2023-02-26T16:44:15.9033667Z Completed true true false 2023-02-23T14:01:42.5172342Z

Remarks

If the materialized view does not exist, this command behaves just like .create materialized-view.

For more information, see the Query parameter and Properties sections.

Limitations

  • Changes not supported:

    • Changes to the materialized view group by expressions.
    • Changing column type.
    • Renaming columns. For example, altering a view of T | summarize count() by Id to T | summarize Count=count() by Id drops column count_ and creates a new column Count, which initially contains nulls only.

  • Impact on existing data:

    • Altering the materialized view has no impact on existing data.
    • Adding filters to the query applies only to newly ingested records, and doesn't change records that have already been materialized.
      • New columns receive nulls for all existing records until records ingested after the alter command modify the null values.
      • For example: A view of T | summarize count() by bin(Timestamp, 1d) is altered to T | summarize count(), sum(Value) by bin(Timestamp, 1d). For a particular Timestamp=T for which records have already been processed before altering the view, the sum column contains partial data. This view only includes records processed after the alter execution.