The use of an identity column in a Delta table affects the execution of a MERGE statement by disabling concurrent transactions. This constraint means that when performing operations such as upserting or deleting data, the identity column enforces that the operations must be executed sequentially, even if they originate from a single session. This is because identity columns in Delta Lake are designed to assign unique values to each record, which requires sequential processing to ensure uniqueness. • As a result, the identity column constraint impacts the internal workings of a MERGE statement by potentially enforcing sequential writes, even when the operation is performed from a single session. This design choice is necessary to maintain the integrity and uniqueness of the identity values assigned to records.
