[DRILL-5099] support OFFSET values greater than one, for LEAD & LAG window functions

• Type: Bug
• Status: Open
• Priority: Minor
• Resolution: Unresolved
• Affects Version/s: 1.9.0
• Component/s: Execution - Flow
• Labels: window_function
• Assignee: Unassigned
• Reporter: Khurram Faraaz
• Created: 03/Dec/16 18:41
• Updated: 27/Mar/17 10:30

Description

Provide support for OFFSET values greater than one, for LEAD & LAG window functions.

Adding adeneche comments from the dev list here

Things that need to be done to make Lag (or Lead) support offsets other
than 1:
- WindowFunction.Lead should extract the offset value from its FunctionCall
argument, you can look at WindowFunctionNtile.numTilesFromExpression() for
and example on how to do that.
- make sure calls to copyNext() and copyPrev() in NoFrameSupportTemplate
use the offset and not the hard coded value (you already figured that out)
- finally make sure you update UnsupportedOperatorsVisitor to no longer
throw an exception when we pass an offset value other than 1 to Lead or
Lag. Just search for DRILL-3596 in that class and you will find the if
block that need to be removed

I think this should be enough to get it to work in the general case.