Iceberg table merge into delete support

[rongfengliang]

Currently, Dremio not support merge into with delete

MERGE | Dremio Documentation

but other engine (spark ) support

https://iceberg.apache.org/docs/latest/spark-writes/#merge-into

WHEN MATCHED AND s.op = 'delete' THEN DELETE
WHEN MATCHED AND t.count IS NULL AND s.op = 'increment' THEN UPDATE SET t.count = 0
WHEN MATCHED AND s.op = 'increment' THEN UPDATE SET t.count = t.count + 1