Question

我在mysql中有一个查询，它给了我这个

product    count(*)
-------    ---------
A           5
B           2
C           3
D           4
E           1

查询很简单，如

select product,count(*) from dashboard group by product;

现在问题是我想将某些产品的数量合并到其他产品中，例如预期的输出是

product    count(*)
-------    ---------
A           7
C           3
D           5

所以计数（A）=计数（A）+计数（B）

count（c）= count（C）

count（D）= count（D）+ count（E）

我在想这样的事情

select case
when product = 'A' OR product = 'B' then ----
when product = 'C' then ----
end

Answer 1

第二次对现有结果进行分组（这具有显着优势，即如果可能的话，它将使用索引执行第一个聚合，然后使用较小的结果集执行第二个更简单的总和）：

SELECT   CASE
           WHEN p IN ('A','B') THEN 'A'
           WHEN p IN ('C')     THEN 'C'
           WHEN p IN ('D','E') THEN 'D'
         END AS product, SUM(c)
FROM     (
           SELECT   product AS p, COUNT(*) AS c
           FROM     dashboard
           GROUP BY p
         ) t
GROUP BY product

在sqlfiddle上查看。

Answer 2

您可以在子查询中将更改放置到产品中：

select product, count(*) Total
from
(
  select 
    case
        when product in ('A','B') then 'A'
        when product in ('C')     then 'C'
        when product in ('D','E') then 'D'
     end AS product
  from dashboard
) src
group by product;

请参阅SQL Fiddle with Demo

mysql查询添加多行条目

2 个答案: