Merge pull request #279872 from jovanpop-msft/patch-244

Serverless is reader level 1

Author: prmerger-automator[bot]

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

@@ -877,12 +877,23 @@ 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 are compatible with **Delta reader version 1**.
 - 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).
 
-### Column rename in Delta table is not supported
+### Serverless support Delta 1.0 version
+
+Serverless SQL pools are reading only Delta Lake 1.0 version. Serverless SQL pools is a [Delta reader with level 1](https://github.com/delta-io/delta/blob/master/PROTOCOL.md#reader-version-requirements), and doesn’t support the following features:
+- Column mappings are ignored - serverless SQL pools will return original column names.
+- Delete vectors are ignored and the old version of deleted/updated rows will be returned (possibly wrong results).
+- The following Delta Lake features are not supported: [V2 checkpoints](https://github.com/delta-io/delta/blob/master/PROTOCOL.md#v2-checkpoint-table-feature), [timestamp without timezone](https://github.com/delta-io/delta/blob/master/PROTOCOL.md#timestamp-without-timezone-timestampntz), [VACUUM protocol check](https://github.com/delta-io/delta/blob/master/PROTOCOL.md#vacuum-protocol-check)
+
+#### Delete vectors are ignored
+
+If your Delta lake table is configured to use Delta writer version 7, it will store deleted rows and old versions of updated rows in Delete Vectors (DV). Since serverless SQL pools have Delta reader 1 level, they will ignore the delete vectors and probably produce **wrong results** when reading unsupported Delta Lake version.
+
+#### Column rename in Delta table is not supported
 
 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.