UPDATE statements on Microsoft Azure Synapse are limited to simple FROM clauses, requiring a combination of CREATE TABLE AS SELECT (CTAS) and an implicit JOIN to implement complex source expressions for an UPDATE.
To learn more, see AH. ANSI join for update statements in the Microsoft Azure Synapse Analytics.
Hyper-Q transparently allows existing applications to run complex UPDATE statements against Azure Synapse by automatically breaking the client request into CTAS and UPDATE as recommended in the above referenced article. In addition, the Hyper-Q emulation for UPDATEs ensures that Teradata semantics are maintained, including multiple source rows updating a single target row. To learn more, see About Hyper-Q emulation for simple UPDATE statements on Azure Synapse.