目录

0. 相关文章链接

1. 基本语法

2. 案例实操

2.1. 查看执行计划

2.2. 查看详细执行计划

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0. 相关文章链接

 Hive文章汇总 

1. 基本语法

EXPLAIN [EXTENDED | DEPENDENCY | AUTHORIZATION] query-sql

2. 案例实操

2.1. 查看执行计划

1）没有生成MR任务的

hive (default)> explain select * from emp;
Explain
STAGE DEPENDENCIES:
  Stage-0 is a root stage

STAGE PLANS:
  Stage: Stage-0
    Fetch Operator
      limit: -1
      Processor Tree:
        TableScan
          alias: emp
          Statistics: Num rows: 1 Data size: 7020 Basic stats: COMPLETE Column stats: NONE
          Select Operator
            expressions: empno (type: int), ename (type: string), job (type: string), mgr (type: int), hiredate (type: string), sal (type: double), comm (type: double), deptno (type: int)
            outputColumnNames: _col0, _col1, _col2, _col3, _col4, _col5, _col6, _col7
            Statistics: Num rows: 1 Data size: 7020 Basic stats: COMPLETE Column stats: NONE
            ListSink

 2）有生成MR任务的

hive (default)> explain select deptno, avg(sal) avg_sal from emp group by deptno;
Explain
STAGE DEPENDENCIES:
  Stage-1 is a root stage
  Stage-0 depends on stages: Stage-1

STAGE PLANS:
  Stage: Stage-1
    Map Reduce
      Map Operator Tree:
          TableScan
            alias: emp
            Statistics: Num rows: 1 Data size: 7020 Basic stats: COMPLETE Column stats: NONE
            Select Operator
              expressions: sal (type: double), deptno (type: int)
              outputColumnNames: sal, deptno
              Statistics: Num rows: 1 Data size: 7020 Basic stats: COMPLETE Column stats: NONE
              Group By Operator
                aggregations: sum(sal), count(sal)
                keys: deptno (type: int)
                mode: hash
                outputColumnNames: _col0, _col1, _col2
                Statistics: Num rows: 1 Data size: 7020 Basic stats: COMPLETE Column stats: NONE
                Reduce Output Operator
                  key expressions: _col0 (type: int)
                  sort order: +
                  Map-reduce partition columns: _col0 (type: int)
                  Statistics: Num rows: 1 Data size: 7020 Basic stats: COMPLETE Column stats: NONE
                  value expressions: _col1 (type: double), _col2 (type: bigint)
      Execution mode: vectorized
      Reduce Operator Tree:
        Group By Operator
          aggregations: sum(VALUE._col0), count(VALUE._col1)
          keys: KEY._col0 (type: int)
          mode: mergepartial
          outputColumnNames: _col0, _col1, _col2
          Statistics: Num rows: 1 Data size: 7020 Basic stats: COMPLETE Column stats: NONE
          Select Operator
            expressions: _col0 (type: int), (_col1 / _col2) (type: double)
            outputColumnNames: _col0, _col1
            Statistics: Num rows: 1 Data size: 7020 Basic stats: COMPLETE Column stats: NONE
            File Output Operator
              compressed: false
              Statistics: Num rows: 1 Data size: 7020 Basic stats: COMPLETE Column stats: NONE
              table:
                  input format: org.apache.hadoop.mapred.SequenceFileInputFormat
                  output format: org.apache.hadoop.hive.ql.io.HiveSequenceFileOutputFormat
                  serde: org.apache.hadoop.hive.serde2.lazy.LazySimpleSerDe

  Stage: Stage-0
    Fetch Operator
      limit: -1
      Processor Tree:
        ListSink

2.2. 查看详细执行计划

添加关键词 extended 

hive (default)> explain extended select * from emp;
hive (default)> explain extended select deptno, avg(sal) avg_sal from emp group by deptno;

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