SQL如何通过子查询合并操作计算各类商品销量占总销量的百分比

你可以直接把第一步的分组统计查询作为子查询，嵌套到第二步的FROM子句中即可，逻辑和你分两步执行完全一致，写法如下：

SELECT *, 
    ROUND(CAST(sold_shoes AS FLOAT)/CAST(sold_total AS FLOAT)*100,2) AS sold_shoes_perc,
    ROUND(CAST(sold_gloves AS FLOAT)/CAST(sold_total AS FLOAT)*100,2) AS sold_gloves_perc,
    ROUND(CAST(sold_trousers AS FLOAT)/CAST(sold_total AS FLOAT)*100,2) AS sold_trousers_perc
FROM (
    SELECT stores,
      SUM(shoes) AS sold_shoes,
      SUM(gloves) AS sold_gloves,
      SUM(trousers) AS sold_trousers,
      SUM(shoes) + SUM(gloves) + SUM(trousers) AS sold_total
    FROM t
    GROUP BY stores
) AS t_new

如果你的数据库支持CTE（公用表表达式，MySQL 8.0+、PostgreSQL、SQLite、SQL Server等主流数据库均支持），也可以用CTE写法，逻辑分层更清晰，后续调整更方便：

WITH t_new AS (
    SELECT stores,
      SUM(shoes) AS sold_shoes,
      SUM(gloves) AS sold_gloves,
      SUM(trousers) AS sold_trousers,
      SUM(shoes) + SUM(gloves) + SUM(trousers) AS sold_total
    FROM t
    GROUP BY stores
)
SELECT *, 
    ROUND(CAST(sold_shoes AS FLOAT)/CAST(sold_total AS FLOAT)*100,2) AS sold_shoes_perc,
    ROUND(CAST(sold_gloves AS FLOAT)/CAST(sold_total AS FLOAT)*100,2) AS sold_gloves_perc,
    ROUND(CAST(sold_trousers AS FLOAT)/CAST(sold_total AS FLOAT)*100,2) AS sold_trousers_perc
FROM t_new

内容的提问来源于stack exchange，提问作者ConcreteJungle