Merge pull request #211534 from jovanpop-msft/patch-236

Clarified native CETAS scenario

Author: prmerger-automator[bot]

articles/synapse-analytics/sql/develop-tables-external-tables.md

@@ -16,8 +16,8 @@ ms.custom: ignite-fall-2021
 An external table points to data located in Hadoop, Azure Storage blob, or Azure Data Lake Storage. External tables are used to read data from files or write data to files in Azure Storage. With Synapse SQL, you can use external tables to read external data using dedicated SQL pool or serverless SQL pool.
 
 Depending on the type of the external data source, you can use two types of external tables:
-- Hadoop external tables that you can use to read and export data in various data formats such as CSV, Parquet, and ORC. Hadoop external tables are available in dedicated SQL pools, but they aren't available in serverless SQL pools.
-- Native external tables that you can use to read and export data in various data formats such as CSV and Parquet. Native external tables are available in serverless SQL pools, and they are in **public preview** in dedicated SQL pools.
+- **Hadoop external tables** that you can use to read and export data in various data formats such as CSV, Parquet, and ORC. Hadoop external tables are available in dedicated SQL pools, but they aren't available in serverless SQL pools.
+- **Native external tables** that you can use to read and export data in various data formats such as CSV and Parquet. Native external tables are available in serverless SQL pools, and they are in **public preview** in dedicated SQL pools. Writing/exporting data using CETAS and the native external tables is available only in the serverless SQL pool, but not in the dedicated SQL pools.
 
 The key differences between Hadoop and native external tables are presented in the following table:
 
@@ -32,6 +32,7 @@ The key differences between Hadoop and native external tables are presented in t
 | Recursive folder scan | Yes | Yes. In serverless SQL pools must be specified `/**` at the end of the location path. In Dedicated pool the folders are alwasy scanned recursively. |
 | Storage authentication | Storage Access Key(SAK), AAD passthrough, Managed identity, Custom application Azure AD identity | [Shared Access Signature(SAS)](develop-storage-files-storage-access-control.md?tabs=shared-access-signature), [AAD passthrough](develop-storage-files-storage-access-control.md?tabs=user-identity), [Managed identity](develop-storage-files-storage-access-control.md?tabs=managed-identity), [Custom application Azure AD identity](develop-storage-files-storage-access-control.md?tabs=service-principal). |
 | Column mapping | Ordinal - the columns in the external table definition are mapped to the columns in the underlying Parquet files by position. | Serverless pool: by name. The columns in the external table definition are mapped to the columns in the underlying Parquet files by column name matching. <br/> Dedicated pool: ordinal matching. The columns in the external table definition are mapped to the columns in the underlying Parquet files by position.|
+| CETAS (exporting/transformation) | Yes | CETAS with the native tables as a target works only in the serverless SQL pool. You cannot use the dedicated SQL pools to export data using native tables. |
 
 > [!NOTE]
 > The native external tables are the recommended solution in the pools where they are generally available. If you need to access external data, always use the native tables in serverless pools. In dedicated pools, you should switch to the native tables for reading Parquet files once they are in GA. Use the Hadoop tables only if you need to access some types that are not supported in native external tables (for example - ORC, RC), or if the native version is not available.