SQL Server 2008，如何检查数据库中是否存在多条记录？

Question

我有 3 张桌子：

• 配方：
  • 身份证、姓名
• 成分：
  • 身份证、姓名
• 配方成分：
  • id、recipeId、componentId、数量

每次客户创建新配方时，我都需要检查recipeingredient 表以验证此配方是否存在。如果ingredientId 和quantity 完全一样，我会告诉客户配方已经存在。由于我需要检查多行，因此需要帮助来编写此查询。

Answer 1

了解您的成分和数量后，您可以执行以下操作：

select recipeId as ExistingRecipeID
from recipeingredient
where (ingredientId = 1 and quantity = 1)
    or (ingredientId = 8 and quantity = 1)
    or (ingredientId = 13 and quantity = 1)
group by recipeId
having count(*) = 3 --must match # of ingeredients in WHERE clause

Answer 2

我原本以为下面的查询会找到成分完全相同的食谱对：

select ri1.recipeId, ri2.recipeId
from RecipeIngredient ri1 full outer join
     RecipeIngredient ri2
     on ri1.ingredientId = ri2.ingredientId and
        ri1.quantity = ri2.quantity and
        ri1.recipeId < ri2.recipeId
group by ri1.recipeId, ri2.recipeId
having count(ri1.id) = count(ri2.id) and   -- same number of ingredients
       count(ri1.id) = count(*) and        -- all r1 ingredients are present
       count(*) = count(ri2.id)            -- all r2 ingredents are present

但是，此查询无法正确计算事物，因为不匹配项没有正确的 id 对。唉。

以下确实进行了正确的比较。它在连接之前计算每个配方中的成分，因此可以在所有匹配的行上比较该值。

select ri1.recipeId, ri2.recipeId
from (select ri.*, COUNT(*) over (partition by recipeid) as numingredients
      from @RecipeIngredient ri
     ) ri1 full outer join
     (select ri.*, COUNT(*) over (partition by recipeid) as numingredients
      from @RecipeIngredient ri
     ) ri2
     on ri1.ingredientId = ri2.ingredientId and
        ri1.quantity = ri2.quantity and
        ri1.recipeId < ri2.recipeId
group by ri1.recipeId, ri2.recipeId
having max(ri1.numingredients) = max(ri2.numingredients) and
       max(ri1.numingredients) = count(*)

having 子句保证每个配方的成分数量相同，并且匹配成分的数量是总数。这一次，我在以下数据上进行了测试：

insert into @recipeingredient select 1, 1, 1
insert into @recipeingredient select 1, 2, 10
insert into @recipeingredient select 2, 1, 1
insert into @recipeingredient select 2, 2, 10
insert into @recipeingredient select 2, 3, 10
insert into @recipeingredient select 3, 1, 1
insert into @recipeingredient select 4, 1, 1
insert into @recipeingredient select 4, 3, 10
insert into @recipeingredient select 5, 1, 1
insert into @recipeingredient select 5, 2, 10

如果您有新配方，您可以修改此查询，使用on 子句上的附加条件，仅在其中一个表（例如 ri1）中查找配方。

如果您将配料放在临时表中，您可以用新表替换其中一个表，例如 ri1。

Answer 3

您可以尝试这样的方法来查找是否有重复：

-- Setup test data
declare @recipeingredient table (
      id int not null primary key identity
    , recipeId int not null
    , ingredientId int not null
    , quantity int not null
)
insert into @recipeingredient select 1, 1, 1
insert into @recipeingredient select 1, 2, 10
insert into @recipeingredient select 2, 1, 1
insert into @recipeingredient select 2, 2, 10

-- Actual Query
if exists (
    select *
    from @recipeingredient old
        full outer join @recipeingredient new
            on old.recipeId != new.recipeId         -- Different recipes
            and old.ingredientId = new.ingredientId -- but same ingredients
            and old.quantity = new.quantity         -- and same quantities
    where old.id is null    -- Match not found
        or new.id is null   -- Match not found
)
begin
    select cast(0 as bit) as IsDuplicateRecipe
end
else begin
    select cast(1 as bit) as IsDuplicateRecipe
end

由于这实际上只是在搜索重复项，因此您可能需要用临时表或 pass a table variable 替换“新”表。这样您就不必在进行搜索之前插入新记录。您还可以插入基表，将整个事物包装在事务中并根据结果回滚。