GROUP BY与COUNT选择值 [英] GROUP BY with COUNT select value

问题描述

这是我的查询

  SELECT  
 prod.dep_ID，
 dep.dep_Name，
 cat.cat_Description，
 prod.prod_Description 
  FROM  
 tblProduct  AS  prod，appCategory  AS  cat，tblDepartment  AS  dep 
 < span class =code-keyword> WHERE  prod.dep_ID =  @ dep_ID  
  AND  prod.dep_ID = dep.dep_ID 

现在我想计算每个cat_Description的总产品。

我该怎么做？

解决方案

最佳猜测：

  SELECT  prod.dep_ID，dep.dep_Name，cat.cat_Description，COUNT（prod.prod_Description） AS  CountOfProductsInCategory 
  FROM  tblProduct  AS  prod  INNER | LEFT | RIGHT   JOIN  appCategory  AS  cat  ON  ... 
  INNER | LEFT | RIGHT   JOIN  tblDepartment  AS  dep  ON  prod.dep_ID = dep.dep_ID 
  WHERE  prod.dep_ID =  @dep_ID  
  GROUP   BY  prod.dep_ID，dep.dep_Name，cat。 cat_Description 

注意：我正在使用连接将数据连接到单个结果集中。加入数据的方法很少。请阅读本文以找出哪一个最适合您： SQL连接的可视化表示 [ ^ ]

This is my query

SELECT
          prod.dep_ID,
          dep.dep_Name,
          cat.cat_Description,
          prod.prod_Description
      FROM
        tblProduct AS prod, appCategory AS cat, tblDepartment AS dep
        WHERE prod.dep_ID = @dep_ID
        AND prod.dep_ID = dep.dep_ID

Now i want to count the total products of each cat_Description.
How can i do that?

解决方案

Best guess:

SELECT prod.dep_ID, dep.dep_Name, cat.cat_Description, COUNT(prod.prod_Description) AS CountOfProductsInCategory
FROM tblProduct AS prod INNER|LEFT|RIGHT JOIN appCategory AS cat ON ...
INNER|LEFT|RIGHT JOIN tblDepartment AS dep ON prod.dep_ID = dep.dep_ID
WHERE prod.dep_ID = @dep_ID
GROUP BY prod.dep_ID, dep.dep_Name, cat.cat_Description

Note: i'm using joins to join data into single result set. There are few ways to join data. Please read this to find out which one is the best for you: Visual Representation of SQL Joins[^].

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