Question

我正在使用PostgreSQL，我在Result表中有一个名为Job的列，它包含2/3，1/3，2/3等值。

例如：Job表行是：

job_id result
------ ------
1      2/3
2      1/3
3      2/3

我希望以result列的方式应用聚合函数我可以得到如下结果：5/9

但Result属于文字类型列，我们无法直接在该列上应用sum / avg / min / max等功能。< / p>

任何人都可以使用查询本身建议任何其他方法来实现该结果吗？

所有建议都表示赞赏。

感谢。

Answer 1

SELECT SUM( dividend ) || '/' || SUM( divisor )
       AS FractionOfSums
     , AVG( dividend / divisor )        
       AS AverageOfFractions
FROM
  ( SELECT CAST(substr(result, 1, position('/' in result)-1 ) AS int)
           AS dividend
         , CAST(substr(result, position('/' in result)+1 ) AS int)
           AS divisor
    FROM rows
  ) AS division

Answer 2

除了ypercube的优秀答案之外，如果你想简化你需要找到最大公约数的分数。

这是存储函数的伪代码，可以生成：

CREATE FUNCTION gcd(x int, y int) RETURNS int DETERMINISTIC
BEGIN
  DECLARE dividend int;
  DECLARE divisor int;
  DECLARE remainder int;

  SET dividend := GREATEST(x, y);
  SET remainder := LEAST(x, y);

  WHILE remainder != 0 DO
    SET divisor = remainder;
    SET remainder = MOD(dividend, divisor);
    SET dividend = divisor;
  END WHILE;

  RETURN divisor;
END

现在您可以将查询重写为：

SELECT (dividend/MyGCD) || '/' || (divisor/MyGCD) as FractionOfSums
  , AverageOfFractions 
FROM ( 
  SELECT 
    SUM( dividend ) as dividend
    , SUM( divisor ) AS divisor      
    , gcd(SUM( dividend ),SUM( divisor )) as MyGCD 
    , AVG( dividend / divisor ) AS AverageOfFractions 
  FROM ( 
    SELECT CAST(substr(result, 1, position('/', result)-1 ) AS int) AS dividend
        , CAST(substr(result, position('/', result)+1 ) AS int) AS divisor    
    FROM rows ) AS division 
) as Elements

请注意，GCD功能非常慢。

如何在列cotainining字符串值上使用聚合函数？

2 个答案: