[HIVE-20557] Constant Folding: null > (expr) is not constant folded to NULL

• Type: Improvement
• Status: Open
• Priority: Major
• Resolution: Unresolved
• Affects Version/s: 3.1.0, 4.0.0
• Component/s: CBO
• Assignee: Unassigned
• Reporter: Gopal Vijayaraghavan
• Created: 14/Sep/18 03:28
• Updated: 12/Oct/18 13:42

Description

create temporary table foo(col1 int, col2 int, col3 int, col5 int, col9 int) stored as orc;

explain select count(1) from foo where 
CASE WHEN (col5 is not null) THEN (((col1 / col5) > (col9 / col3))) ELSE ((null > (col9 / col3))) END;

explain select count(1), max((col9/col3) > null) from foo where 
CASE WHEN (col5 is not null) THEN (((col1 / col5) > (col9 / col3))) ELSE (((col9 / col3) > null)) END;

There's no sane way to write this query, but this is actually generated by CBO for an expression which looks like

case when t_w_firstyear.year_total > 0 then t_w_secyear.year_total / t_w_firstyear.year_total else null end
           > case when t_s_firstyear.year_total > 0 then t_s_secyear.year_total / t_s_firstyear.year_total else null end

Issue Links

• is related to: CALCITE-2555 RexSimplify: >=(true, null) could be simplified to null