mysql - 在选择中的计算中使用连接计数

Question

SELECT e.qty * e.unit_cost * e.unit_no * (e.factor/100) AS Ext_price, c.cost_type, c.cost_dt, c.internal_cost_amt, c.client_cost_amt
FROM equipment e
LEFT JOIN CostAllocation c ON (c.object_row_id = e.row_id)

我现在想用 Ext_price 除以与设备行匹配的 CostAllocation 行数。我该怎么做？

Answer 1

SELECT e.qty*e.unit_cost*e.unit_no*e.factor/(100*x.cnt) AS Ext_price,
       c.cost_type,
       c.cost_dt,
       c.internal_cost_amt,
       c.client_cost_amt
FROM equipment e
LEFT JOIN CostAllocation c ON c.object_row_id = e.row_id
LEFT JOIN
  (SELECT row_id,
          count(*) cnt
   FROM CostAllocation
   GROUP BY row_id) x ON c.object_row_id = x.row_id