[FLINK-19830] Properly implements processing-time temporal table join

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Component/s: Table SQL / Runtime
• Assignee: Leonard Xu
• Reporter: Leonard Xu
• Created: 27/Oct/20 11:35
• Updated: 27/Jun/23 03:24

Description

The exsiting TemporalProcessTimeJoinOperator has already supported temporal table join.
However, the semantic of this implementation is problematic, because the join processing for left stream doesn't wait for the complete snapshot of temporal table, this may mislead users in production environment.

Under the processing time temporal join semantics, to get the complete snapshot of temporal table may need introduce new mechanism in FLINK SQL in the future.

*Background* :

• The reason why we turn off the switch[1] for `FOR SYSTEM_TIME AS OF` syntax for temporal table join is only the semantic consideration as above.
• The reason why we turn on temporal table function  is that it has been alive for a long time, thus although it exists same semantic problem, but we still support it from the perspective of compatibility.

[1] https://github.com/apache/flink/blob/4fe9f525a92319acc1e3434bebed601306f7a16f/flink-table/flink-table-planner/src/main/java/org/apache/flink/table/planner/plan/nodes/exec/stream/StreamExecTemporalJoin.java#L257