Question

我有一张有动物的桌子

CREATE TABLE Animals
(
AnimalId int NOT NULL,
Color int NOT NULL,
Breed int NOT NULL,
Genre int NOT NULL,
);

表格完全相同但一切都是可选的（除了密钥）

CREATE TABLE Expenses
(
ExpenseId int NOT NULL,
Color int,
Breed int,
Genre int,
);

最后是一对多表：

CREATE TABLE AnimalsExpenses
(
ExpenseId int NOT NULL FOREIGN KEY REFERENCES Expenses(ExpenseId),
AnimalId int NOT NULL FOREIGN KEY REFERENCES Animals(AnimalId),
);

如果

，记录（a，e）应该在AnimalExpenses表上

((SELECT Color FROM Animals WHERE AnimalId = a) = (SELECT Color FROM Expenses WHERE ExpenseId = e)
OR (NULL) = (SELECT Color FROM Expenses WHERE ExpenseId = e))
AND
((SELECT Breed FROM Animals WHERE AnimalId = a) = (SELECT Breed FROM Expenses WHERE ExpenseId = e)
OR (NULL) = (SELECT Breed FROM Expenses WHERE ExpenseId = e))
AND
((SELECT Genre FROM Animals WHERE AnimalId = a) = (SELECT Genre FROM Expenses WHERE ExpenseId = e)
OR (NULL) = (SELECT Genre FROM Expenses WHERE ExpenseId = e))

...如何更新AnimalsExpenses的查询？那就是：它删除不应该在n-m表上的记录，并添加那些需要在那里的记录

示例：

------ Animals -------------------
 AnimalId  Color  Breed  Genre
----------------------------------
     1      1       1      1
     2      1       1      2
     3      1       2      2

----- Expenses -------------------
 ExpenseId  Color  Breed  Genre
----------------------------------
     1       NULL   NULL   NULL      (applies to every animal)
     2       NULL    2     NULL      (applies to animals of breed 2)
     3         1     2      2        (applies exactly to animal 3)

----- AnimalsExpenses -------------------------------------------
  AnimalId   ExpenseId   Is it ok?
-----------------------------------------------------------------
      1        1         yes, because "expense 1" applies to all
      2        1         yes, because "expense 1" applies to all
      3        1         yes, because "expense 1" applies to all

      1        2         no, breed doesnt match
      2        2         no, breed doesnt match
      3        2         yes, because "expense 2" matches breed with "animal 3"

      1        3         no, breed and genre doesnt match
      2        3         no, breed doesnt match
      3        3         yes, everything matches

Answer 1

为什么不截断表格然后运行

Insert into AnimalsExpenses
select a.AnimalId
  , e.ExpenseId
  from Animals a
  inner join Expenses e on a.Breed = ISNULL(e.Breed, a.Breed) 
          AND a.Color = ISNULL(e.Color, a.Color) 
          AND a.Genre = ISNULL(e.Genre, a.Genre)

Answer 2

我建议您以这种方式重写WHERE条件：

ISNULL(Expenses.Color, Animals.Color) = Animals.Color
AND ISNULL(Expenses.Breed, Animals.Breed) = Animals.Breed
AND ISNULL(Expenses.Genre, Animals.Genre) = Animals.Genre

另请参阅COALESCE。

使用SQL更新多对多表

2 个答案: