sql - 选择 TOP 2 导致变量没有循环

Question

我想将前 2 个结果存储在 2 个变量中。

创建表 t(id int);
插入 t (id) 值 (1),(2),(3),(4);
    
声明@id1 int
声明@id2 int

选择前 2 个 @id1 = 第一个 id，
             @id2 = 下一个 id
从T

SQLFiddle

我可以在一个查询中完成它而不使用循环吗？

Answer 1

declare @id1 int,@id2 int

;with cte as (
  select top (2) id
  from t
  order by id
)
select @id1 = min(id), @id2 = max(id)
from cte

select @id1,@id2

小提琴演示

Answer 2

with cte as (
    select top 2 id, row_number() over(order by id) as rn
    from t
    order by id
)
select
    @id1 = (select id from cte where rn = 1),
    @id2 = (select id from cte where rn = 2)

或者

with cte as (
    select top 2 id, row_number() over(order by id) as rn
    from t
    order by id
)
select
    @id1 = max(case when rn = 1 then id end),
    @id2 = max(case when rn = 2 then id end)
from cte

sql fiddle demo

Answer 3

您可以LEAD()用于 SQL Server 2012。

SELECT TOP 1 @id1 = ID, @id2 = LEAD(ID) OVER (ORDER BY ID) FROM t

• SQLFiddle 演示

Answer 4

使用两个 SELECT 很容易......

DECLARE @id1 INT
DECLARE @id2 INT

SELECT TOP 1 @id1 = x.id 
    FROM (SELECT *, ROW_NUMBER() OVER (ORDER BY id) RN FROM t) x 
WHERE x.RN = 1

SELECT TOP 1 @id2 = x.id 
    FROM (SELECT *, ROW_NUMBER() OVER (ORDER BY id) RN FROM t) x 
WHERE x.RN = 2

SELECT @id1, @id2

使用 SQL 2012，您显然可以

SELECT @id1 = id 
    FROM t ORDER BY id OFFSET 0 ROWS FETCH NEXT 1 ROWS ONLY

SELECT @id2 = id 
    FROM t ORDER BY id OFFSET 1 ROWS FETCH NEXT 1 ROWS ONLY

或者即使在 2008 年，你也可以

; WITH Base AS (
    SELECT *, ROW_NUMBER() OVER (ORDER BY id) RN FROM t   
)

SELECT @id1 = b1.id, @id2 = b2.id
    FROM Base b1, Base b2
    WHERE b1.RN = 1 AND B2.RN = 2

Answer 5

declare @id1 int
declare @id2 int

declare @table table(id int,rownum int)

insert into @table
select top 2 id,row_number() over( order by id) as rn from t

select @id1=case rownum when 1 then id else @id1 end,
@id2=case rownum when 2 then id end from @table

select @id1,@id2

SQL 小提琴

Answer 6

2个选择更简单的方法：

declare @id1 int
declare @id2 int
select top 1 @id1 = id from t
select top 2 @id2 = id from t
select @id1, @id2

SQL小提琴