Brett Powell has a procedure for us:
This post provides an example of a stored procedure which A) identifies the last two partitions of an Azure Synapse Analytics SQL pool table (which uses the columnstore index (default)) and B) rebuilds the index for these two partitions. Additionally, a sample PowerShell-based Azure Automation runbook is included for scheduling the execution of this procedure.
This post follows up on the previous post regarding a Power BI template to be used to analyze the health or quality of a columnstore index. For example, the template shared may help you find that the last one or two partitions such as partition numbers 39 and 40 out of 40 partitions may have many open (uncompressed) and/or not-optimized rowgroups. The cause of these low quality partitions could be that recent and ongoing data processing events are impacting these partitions (inserts,updates). Perhaps partitions 39 and 40 refer to the current and prior month for example.
Read on for the link to the script, as well as details on how to use it.