Impala查询参数 APPX_COUNT_DISTINCT

zhiliang-chen

于 2019-10-25 12:15:15 发布

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文章标签： impala appx_count_distinct

原文链接：https://docs.cloudera.com/documentation/enterprise/5-15-x/topics/impala_appx_count_distinct.html

版权

允许在单条查询中有多个COUNT(DISTINCT)操作,通过在内部重写COUNT(DISTINCT)为NDV()函数;
获得的结果是近似的;

默认,一条查询只能有一个COUNT(DISTINCT)

CDH 5.2以上支持;

值: Boolean;0或false;1或true;其他值解释为false;

默认值: false(set语句显示为0)

实例

> select count(distinct x) from int_t;
> select count(distinct property) from int_t;

//# 多条count(distinct)会报错
> select count(distinct x), count(distinct property) from int_t;
ERROR: AnalysisException: all DISTINCT aggregate functions need to have the same set of parameters
as count(DISTINCT x); deviating function: count(DISTINCT property)

//# 开启查询参数
> set APPX_COUNT_DISTINCT=true;
> select count(distinct x), count(distinct property) from int_t;