Hi, I'd like to understand a little more how joins work. I have a fairly simple LEFT JOIN query, and I'm seeing spotty results on the joins. I know there is a record on the right side, but sometimes it produces a result, and sometimes it doesn't.
Sample query: SELECT a.id, b.val1, c.val2 FROM table1 a LEFT JOIN table2 b ON a.bId = b.Id LEFT JOIN table3 c ON a.cId = c.Id I'm using Flink 1.13.2. All tables are loaded from kafka. Using the Table/SQL API. My suspicion is that the distributed nature of the join causes the problem. If I reduce the parallelism to match the number of slots, resulting in a single task manager, the joins always (I think) seem to work. So, my assumption is that records in table3 that should join to table1 are not present on the same task manager, so the join produces null values for table3. I thought there might be a way to specify the partitioning. If the tables are from a multi-tenant database, I could specify the tenant-id as the partition key, but the Flink SQL "PARTITION BY" statement doesn't seem to work that way. Is there a way to confirm this? Does anyone know if this is a known problem, and is there a solution? Thanks, Curt
