查询变量

Question

是否可以在查询中设置/读取变量？

伪代码:

SELECT animal_name,
    @tallest_animal = (select top 1 height from animal order by height desc) as tallest,
    @smallest_animal = (select top 1 height from  animal order by height asc) as smallest
FROM animals
WHERE height BETWEEN @smallest_animal AND @tallest_animal

我知道结果可以通过使查询不同来实现,我的问题的实际用法很难解释.

它是有问题的Microsoft SQL Server.:)

Answer 1

是的,您可以在查询中设置变量.你的语法实际上非常接近.

为此,您需要:

SELECT @YourVariable = Column
FROM Animals

注意:在为变量分配字段时,不能使用AS.

您必须确保将查询中的所有字段分配给变量,否则您将收到以下错误:

为变量赋值的SELECT语句不能与数据检索操作结合使用.

要解决此问题,只需将AnimalName分配给@AnimalName变量即可.

编辑:

DECLARE @AnimalName  VARCHAR(20)
DECLARE @TallestAnimal  INT
DECLARE @SmallestAnimal INT

SELECT @AnimalName = animal_name,
   @TallestAnimal  = (select top 1 height from animal order by height desc),
   @SmallestAnimal = (select top 1 height from  animal order by height asc) 
FROM animals
WHERE height BETWEEN @SmallestAnimal AND @TallestAnimal 

此代码假设高度字段的类型为INT.

Answer 2

不，不可能，而是这样使用：

DECLARE @tallest_animal int, @smallest_animal int
SET @tallest_animal=(SELECT max(height) from animals)
SET @smallest_animal=(SELECT min(height) from animals)
SELECT animal_name from animals where height between @tallest_animal AND @smallest_animal

这样的事情会起作用，但是我不确定您在寻找什么。

Answer 3

您可以使用派生表而不是变量.

select A.animal_name, M.tallest, M.smallest
from animals A
  inner join 
      (
        select max(height) as tallest,
               min(height) as smallest
        from animal
      ) M
    on A.height between M.smallest and M.tallest