SQL中的复杂求和

我正在使用一个使用SQL99的关系数据库

我有一系列的10列，每10列包含一个数值

我需要对每一列分别求和，然后将这些总和相加，得到一个总的总和。然后我必须把总数除以15

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我尝试了我能想到的每种格式，但还没有返回任何结果。我不知道语法应该是什么样子。

您只想返回一行吗？多行，按uuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuuu。。。比我的版本更好！当心空值，加入几个COALESC（）或IFNULL（）

SELECT SUM(col1), SUM(col2)..., SUM(col1 + col2 + col3 + col4...)/15
FROM TABLENAME
GROUP BY 1=1

SELECT SUM(subsum) / 15 FROM (
   SELECT SUM(column1) AS subsum
      FROM table
     UNION ALL
    SELECT SUM(column2) AS subsum
      FROM table
     UNION ALL
    ...
    SELECT SUM(column10) AS subsum
      FROM table
)

select 
      sum(col1) as sum1, 
      sum(col2) as sum2, 
      sum(col3) as sum3, 
      sum(col4) as sum4,
      sum(col5) as sum5, 
      sum(col6) as sum6, 
      sum(col7) as sum7, 
      sum(col8) as sum8,
      sum(col9) as sum9, 
      sum(col10) as as sum10,
      sum( col1 + col2 + col3 + col4 + col5 + col6 + col7 + col8 + col9 + col10) as overallsum,
      sum( col1 + col2 + col3 + col4 + col5 + col6 + col7 + col8 + col9 + col10) / 15 as dividedsum
   from 
      tablename