Hive count(*) count(1) count(c1) 区别

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1 count(c1) 不统计c1=NULL的记录，但统计c1='' 和 c1=' ' 空格的记录！

2 count(*) = count(1) = count(10000) = count(c1) + count(*) where c1 is null 

3 count(数字)，这个数字可以设置任意的正整数，不影响结果。

          select count(1)from (select 1 as c1 union allselect '' as c1union allselect null as c1) t1  -- 3 行select count(1)from (select 1 as c1 union allselect '' as c1union allselect ' ' as c1 -- 空格union allselect null as c1) t1  -- 4 行--------------select count(*)from (

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