[HIVE-20850] Push case conditional from projections to dimension tables if possible

• Type: Improvement
• Status: Closed
• Priority: Major
• Resolution: Fixed
• Fix Version/s: 4.0.0-alpha-1
• Assignee: Zoltan Haindrich
• Reporter: Zoltan Haindrich
• Created: 31/Oct/18 21:04
• Updated: 27/Feb/24 22:23
• Resolved: 12/Nov/18 18:07

Description

noticed by gopalv: If there is a project which could be only evaluated after the join; but the condition references only a single column from a small dimension table; hive will end up evaluating the same thing over and over again...

explain
select  s_store_name, s_store_id,
        sum(case when (d_day_name='Sunday') then ss_sales_price else null end) sun_sales,
        sum(case when (d_day_name='Monday') then ss_sales_price else null end) mon_sales,
        sum(case when (d_day_name='Tuesday') then ss_sales_price else  null end) tue_sales,
        sum(case when (d_day_name='Wednesday') then ss_sales_price else null end) wed_sales,
        sum(case when (d_day_name='Thursday') then ss_sales_price else null end) thu_sales,
        sum(case when (d_day_name='Friday') then ss_sales_price else null end) fri_sales,
        sum(case when (d_day_name='Saturday') then ss_sales_price else null end) sat_sales
 from date_dim, store_sales, store
 where d_date_sk = ss_sold_date_sk and
       s_store_sk = ss_store_sk and
       s_gmt_offset = -6 and
       d_year = 1998 
 group by s_store_name, s_store_id
 order by s_store_name, s_store_id,sun_sales,mon_sales,tue_sales,wed_sales,thu_sales,fri_sales,sat_sales
 limit 100;