sql - 0 行受影响的 SQL 查询消息

Question

我在 Eclipse 的数据库中有这张表：

Recipe = (idR, recipeTitle, prepText, cuisineType, mealType)
Ingredient = (idI, ingrDesc)
RecipIngr = (idR*, idI*)

我正在尝试显示包含最少成分的食谱的标题。到目前为止，这是我的查询：

  SELECT recipetitle, COUNT(*)
  FROM recipe
  GROUP BY recipetitle
  HAVING COUNT(recipetitle) =
  (SELECT MAX(COUNT(ingrdesc))
  FROM ingredient
  GROUP BY recipetitle);

这显示“0行受影响”所以我不知道我做错了什么。有什么帮助吗？

Answer 1

你必须在JOIN你的桌子上计算每个食谱的成分数量：

SELECT
    r.recipeTitle,
    COUNT(*) AS nbOfIng
FROM
    recipe r
JOIN
    RecipIngr ri ON r.idR = ri.idR
GROUP BY
    r.idR, r.recipeTitle
HAVING
    nbOfIng = (
        SELECT
            MAX(COUNT(*))
        FROM
            recipe r2
        JOIN
            RecipIngr ri2 ON r2.idR = ri2.idR
        GROUP BY
            r2.idR
)

但是，我不能 100% 确定这是否可行，因为我不知道您使用的是什么数据库引擎。

Answer 2

根据您的需要选择第一个匹配项或所有匹配项 - 对于 MSSQL。

第一的：

SELECT TOP 1 RecipeTitle      = R.recipeTitle
       ,IngredientCount = COUNT(*)
FROM   Recipe R
INNER JOIN RecipIngr RI ON R.idR = RI.idR
INNER JOIN Ingredient I ON RI.idI = I.idI
    GROUP BY R.recipeTitle

全部：

SELECT dtbl.RecipeTitle
FROM (SELECT RecipeTitle      = R.recipeTitle
       ,IngredientCount = COUNT(*)
           ,rank = rank() OVER (Partition BY R.recipeTitle ORDER BY COUNT(*))
FROM   Recipe R
INNER JOIN RecipIngr RI ON R.idR = RI.idR
INNER JOIN Ingredient I ON RI.idI = I.idI
    GROUP BY R.recipeTitle) dtbl
WHERE dtbl.rank = 1