mysql - 当平均行大于某个数字时用mysql计算行的平均值

Question

我有一个计算行平均值的查询。单行的平均值由非空值组成。好吧，这行得通。我现在想要的是仅在平均值大于某个数字时才计算该行。现在它正在使用所有行。我怎样才能完成这项工作？

id | p_cijfer | b_cijfer | c_cijfer | c_id
----------------------------------------------
1  | 4        | 4        |    0     |   3   average = 4
----------------------------------------------
2  | 8        | 6        |    6     |   3   average = 6.7
----------------------------------------------
3  | 10       | 6        |    8     |   3   average = 8
----------------------------------------------
1  | 4        | 4        |    0     |   1   average = 4
----------------------------------------------

现在我只想计算平均值高于 6 的行的平均值。这将导致只计算记录 2 和 3。输出必须是 id 的 2 和 3 的平均值，平均值 = (6.7+8)/2=7.5

select 

AVG(((reviews.prijs_cijfer+
 reviews.planning_cijfer+
 reviews.betrouwbaarheid_cijfer +
 reviews.communicatie_cijfer +
 reviews.kennis_cijfer +
 reviews.innovatie_cijfer
) /
nullif(
  case when prijs_cijfer=0 then 0 else 1 end +
  case when planning_cijfer=0 then 0 else 1 end +
  case when betrouwbaarheid_cijfer=0 then 0 else 1 end +
  case when communicatie_cijfer=0 then 0 else 1 end +
  case when kennis_cijfer=0 then 0 else 1 end +
  case when innovatie_cijfer=0 then 0 else 1 end , 0)))
from reviews

Answer 1

您可以使用子查询来应用过滤器。

select c_id, avg(rows.rowavg) filteredavg, count(rows.rowavg) affecting
from (
    select
        c_id c_id,
        ((reviews.prijs_cijfer+
        reviews.planning_cijfer+
        reviews.betrouwbaarheid_cijfer +
        reviews.communicatie_cijfer +
        reviews.kennis_cijfer +
        reviews.innovatie_cijfer
        ) /
        nullif(
        case when prijs_cijfer=0 then 0 else 1 end +
        case when planning_cijfer=0 then 0 else 1 end +
        case when betrouwbaarheid_cijfer=0 then 0 else 1 end +
        case when communicatie_cijfer=0 then 0 else 1 end +
        case when kennis_cijfer=0 then 0 else 1 end +
        case when innovatie_cijfer=0 then 0 else 1 end , 0)) rowavg
    from reviews
) rows
where rows.rowavg > 6
group by c_id