Major Description
SPARK-30924 adds some check rules for MERGE INTO one of which ensures the first MATCHED clause must have a condition. However, it uses MergeAction.children in the checking which is not accurate for the case, and it lets the below case pass the check:
MERGE INTO testcat1.ns1.ns2.tbl AS target xxx WHEN MATCHED THEN UPDATE SET target.col2 = source.col2 WHEN MATCHED THEN DELETE xxx
We should use MergeAction.condition instead.
