mysql - 多列多重计​​数

Question

我是sql新手。我想计算如下内容:

Select count(*) from table where col1= x and col2=x and Col3=x. 

我需要计算所有不同列中的相同值。 任何帮助将不胜感激。

Answer 1

您可以使用条件聚合:

Select sum(case when col1='x' then 1 else 0 end) as count_col1,
       sum(case when col2='x' then 1 else 0 end) as count_col2,
       sum(case when col3='x' then 1 else 0 end) as count_col3
  from tab;

如果您想获得这些计数值的总和，请将上述查询视为内部查询并使用以下内容:

 Select q.*,
        q.count_col1 + q.count_col2 + q.count_col3 whole_sum
   from     
     (
        Select sum(case when col1='x' then 1 else 0 end) as count_col1,
               sum(case when col2='x' then 1 else 0 end) as count_col2,
               sum(case when col3='x' then 1 else 0 end) as count_col3
          from tab  
      ) q

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