我如何才能从PHP mysql中的两个或多个表中求和字段值

Question

我有六个表，每个表都有两个名为（餐，成本）的列。 我可以合计一桌饭。 但是我想对每张桌子的总和求和。

但是像这样。我有六个桌子。 我想一次汇总每张桌子的费用。

$qq="select SUM(cost5) as 'sumcost' from shawon"; 
$res=mysqli_query($conn,$qq); $data=mysqli_fetch_array($res);  
echo "<div class='container'>". "sum of cost: ".$data['sumcost']."</div>";

有什么办法吗？

Answer 1

您可以使用union all来构建具有相同列均值的唯一表，成本形成六个表中的每个表

select meal, sum(cost)
from (
  select  meal,cost
  from table1 
  union all 
  select  meal,cost
  from table2
  union all 
  select  meal,cost
  from table3
  union all 
  select  meal,cost
  from table4
  union all 
  select  meal,cost
  from table5
  union all 
  select  meal,cost
  from table6
  ) t 
  group by  meal