[HIVE-17342] Where condition with 1=0 should be treated similar to limit 0

• Type: Improvement
• Status: Resolved
• Priority: Minor
• Resolution: Information Provided
• Assignee: Krisztian Kasa
• Reporter: Rajesh Balamohan
• Created: 17/Aug/17 01:19
• Updated: 08/Sep/22 14:45
• Resolved: 31/Aug/22 05:40

Description

In some cases, queries may get executed with where condition mentioning to "1=0" to get schema. E.g

SELECT * FROM (select avg(d_year) as  y from date_dim where d_year>1999) q WHERE 1=0

Currently hive executes the query; it would be good to consider this similar to "limit 0" which does not execute the query.

hive> explain SELECT * FROM (select avg(d_year) as  y from date_dim where d_year>1999) q WHERE 1=0;
OK
Plan optimized by CBO.

Vertex dependency in root stage
Reducer 2 <- Map 1 (CUSTOM_SIMPLE_EDGE)

Stage-0
  Fetch Operator
    limit:-1
    Stage-1
      Reducer 2 vectorized, llap
      File Output Operator [FS_13]
        Group By Operator [GBY_12] (rows=1 width=76)
          Output:["_col0"],aggregations:["avg(VALUE._col0)"]
        <-Map 1 [CUSTOM_SIMPLE_EDGE] vectorized, llap
          PARTITION_ONLY_SHUFFLE [RS_11]
            Group By Operator [GBY_10] (rows=1 width=76)
              Output:["_col0"],aggregations:["avg(d_year)"]
              Filter Operator [FIL_9] (rows=1 width=0)
                predicate:false
                TableScan [TS_0] (rows=1 width=0)
                  default@date_dim,date_dim,Tbl:PARTIAL,Col:NONE,Output:["d_year"]

It does generate 0 splits, but does send a DAG plan to the AM and receive 0 rows as output.

Issue Links

• relates to: HIVE-26524 Use Calcite to remove sections of a query plan known never produces rows