Question

我编写了一个查询，该查询创建了一个新的临时行，其频率显示为id，并且我需要删除所有低于我的频率过滤器要求4的项目。代码按计划工作，直到我添加了where子句（如下）。无法在通常的位置添加where子句的原因是什么？

  SELECT RecipeTitle, COUNT(recipes.RecipeID) AS ingredientsNeeded FROM recipes 
         INNER JOIN recipe_ingredients ON recipe_ingredients.RecipeID = recipes.RecipeID 
              GROUP BY recipes.RecipeID 
              ORDER BY ingredientsNeeded ASC

返回

Calzone | 3 
Hot dog | 2

等

SELECT RecipeTitle, COUNT(recipes.RecipeID) AS ingredientsNeeded FROM recipes 
     INNER JOIN recipe_ingredients ON recipe_ingredients.RecipeID = recipes.RecipeID 
          GROUP BY recipes.RecipeID 
          WHERE ingredientsNeeded < 4
          ORDER BY ingredientsNeeded ASC

您收到错误：

您的SQL语法有错误...请在手册中查找在WHERE附近使用的正确语法...

Answer 1

您应该使用HAVING子句对count进行断言：

SELECT
    r.RecipeTitle,                          -- potentially OK to select this, see below
    COUNT(r.RecipeID) AS ingredientsNeeded
FROM recipes r
INNER JOIN recipe_ingredients ri
    ON ri.RecipeID = r.RecipeID
GROUP BY
    r.RecipeID 
HAVING
    ingredientsNeeded < 4
ORDER BY
    ingredientsNeeded;

请注意，您正在按RecipeID进行汇总，因此从技术上讲，您只能选择或任何汇总。但是，如果RecipeTitle是RecipeID表的主键，则允许选择recipes。

创建临时列时出现WHERE子句问题

1 个答案: