Merge pull request #232946 from jovanpop-msft/patch-240

Delta reader v2 and column mapping are not supported

Author: prmerger-automator[bot]

articles/synapse-analytics/sql/resources-self-help-sql-on-demand.md

@@ -865,6 +865,7 @@ There are some limitations that you might see in Delta Lake support in serverles
 - Serverless SQL pools don't support time travel queries. Use Apache Spark pools in Synapse Analytics to [read historical data](../spark/apache-spark-delta-lake-overview.md?pivots=programming-language-python#read-older-versions-of-data-using-time-travel).
 - Serverless SQL pools don't support updating Delta Lake files. You can use serverless SQL pool to query the latest version of Delta Lake. Use Apache Spark pools in Synapse Analytics to [update Delta Lake](../spark/apache-spark-delta-lake-overview.md?pivots=programming-language-python#update-table-data).
   - You can't [store query results to storage in Delta Lake format](create-external-table-as-select.md) by using the CETAS command. The CETAS command supports only Parquet and CSV as the output formats.
+- Serverless SQL pools in Synapse Analytics are compatible with Delta reader version 1. The Delta features that require Delta readers with version 2 or higher (for example [column mapping](https://github.com/delta-io/delta/blob/master/PROTOCOL.md#reader-requirements-for-column-mapping)) are not supported in the serverless SQL pools.
 - Serverless SQL pools in Synapse Analytics don't support the datasets with the [BLOOM filter](/azure/databricks/optimizations/bloom-filters). The serverless SQL pool ignores the BLOOM filters.
 - Delta Lake support isn't available in dedicated SQL pools. Make sure that you use serverless SQL pools to query Delta Lake files.
 - For more information about known issues with serverless SQL pools, see [Azure Synapse Analytics known issues](../known-issues.md).
@@ -873,6 +874,10 @@ There are some limitations that you might see in Delta Lake support in serverles
 
 The serverless SQL pool does not support querying Delta Lake tables with the [renamed columns](https://docs.delta.io/latest/delta-batch.html#rename-columns). Serverless SQL pool cannot read data from the renamed column.
 
+### The value of a column in the Delta table is NULL
+
+If you are using Delta data set that requires a Delta reader version 2 or higher, and uses the features that are unsupported in version 1 (for example - renaming columns, dropping columns, or column mapping), the values in the referenced columns might not be shown.
+
 ### JSON text isn't properly formatted
 
 This error indicates that serverless SQL pool can't read the Delta Lake transaction log. You'll probably see the following error: