[FLINK-6097] Guaranteed the order of the extracted field references

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Won't Fix
• Component/s: Table SQL / API
• Assignee: sunjincheng
• Reporter: sunjincheng
• Created: 17/Mar/17 08:20
• Updated: 23/Jun/17 15:05
• Resolved: 28/Apr/17 03:29

Description

When we try to implement `OVER window` TableAPI, The first version of the prototype to achieve，we do not consider the table field will be out of order when we implement `translateToPlan` method，then we set `outputRow` field from `inputRow` according to the Initial order of the table field index.
At the beginning, the projections in the select statement less than 5 columns It works well.But Unfortunately when the count of projections bigger than 4 (>=5), we got the random result. Then we debug the code, we find that `ProjectionTranslator # identifyFieldReferences` method uses the` Set` temporary save field, when the number of elements in the Set is less than 5, the Set takes the Se1, Se2, Se3, Se4 data structures. When the number of elements is greater than or equal to 5, the Set takes HashSet # HashTrieSet and which will cause the data to be out of order.
e.g.:
Add the following elements in turn:

A, b, c, d, e
Set (a)
Class scala.collection.immutable.Set $ Set1
Set (a, b)
Class scala.collection.immutable.Set $ Set2
Set (a, b, c)
Class scala.collection.immutable.Set $ Set3
Set (a, b, c, d)
Class scala.collection.immutable.Set $ Set4
// we want (a, b, c, d, e)
Set (e, a, b, c, d) 
Class scala.collection.immutable.HashSet $ HashTrieSet

So we thought 2 approach to solve this problem：

1. Let `ProjectionTranslator # identifyFieldReferences` method guaranteed the order of the extracted field references same as input order.
2. We add the input and output field mapping.

At last we using approach#2 solve the problem. This change is not necessary for the problem i have faced. But I feel it is better to let the output of this method in the same order as the input, it may be very helpful for other cases, though I am currently not aware of any. I am ok with not making this change, but we should add a comment instead to highlight that the potential output of the current output. Otherwise, some people may not pay attention to this and assume it is in order.
Hi, guys, What do you think? Welcome any feedback.

Issue Links

• links to: GitHub Pull Request #3560