获得前N行与在SQL Server 4列

  • Z时代
  • 2024-01-10
  • 分类：问答

假设我有4个列的表格：获得前N行与在SQL Server 4列

Col1 Col2 Col3 Col4

我的初始查询是：

SELECT Col1, Col2, Col3, Col4 
FROM myTable 
ORDER BY Col1, Col2, Col3 DESC, Col4

我期望的结果是所有4列，但与此条件，顶部N Col3不同的行当Col1，Col2是相等的。

实施例具有N = 2：

表的示例数据：

Col1 Col2 Col3 Col4 
--------------------- 
1 a 2000 s 
1 a 2002 c 
1 a 2001 b 
2 b 1998 s 
2 b 2002 c 
2 b 2000 b 
3 c 2000 b 
1 f 1998 n 
1 g 1999 e

期望的结果：

1 a 2002 c 
1 a 2001 b 
1 f 1998 n 
1 g 1999 e 
2 b 2002 c 
2 b 2000 b 
3 c 2000 b

在另一个说明中，当(col1, col2)在多个记录被重复，只是出口顶当按Col3降序排序时，这些记录有N行。

我可以用SQL脚本来做到这一点吗，不用硬编码？

回答：

declare @t table (Col1 int, Col2 char, Col3 int, Col4 char); 
insert into @t values 
(1, 'a', 2000, 's'), 
(1, 'a', 2002, 'c'), 
(1, 'a', 2001, 'b'), 
(2, 'b', 1998, 's'), 
(2, 'b', 2002, 'c'), 
(2, 'b', 2000, 'b'), 
(3, 'c', 2000, 'b'), 
(1, 'f', 1998, 'n'), 
(1, 'g', 1999, 'e'); 
declare @N int = 2; -- number per "top" 
with cte as 
(
select *, 
     row_number() over(partition by col1, col2 order by col3 desc) as rn 
from @t 
) 
select * 
from cte c 
where rn <= @N;

回答：

METHOD FOR 1- MSSQL

http://sqlfiddle.com/#!6/4bda39/6

with a as (
    select ROW_NUMBER() over(partition by t.col1,t.col2 order by t.col3 desc) as row,t.* 
    from myTable as t) 
select * from a where a.row <= 2

替换a.row < = 2（2用N）

METHOD 2-对于MySQL

http://sqlfiddle.com/#!9/79e81a/63

SELECT myTable.Col1, myTable.Col2, myTable.Col3, myTable.Col4 
FROM ( 
    Select Col1 as Col1, Col2 as Col2, count(Col1) as cc, AVG(Col3) as aa 
    From myTable 
    group by Col1, Col2) as tt 
join myTable on myTable.Col1 = tt.Col1 and myTable.Col2 = tt.Col2 
where myTable.Col3 >= tt.aa 
Order by Col1 ,Col2 ,Col3 Desc,Col4

METHOD 3-对于MySQL

http://sqlfiddle.com/#!9/79e81a/79

SELECT * FROM (
    SELECT CASE Col1 
     WHEN @Col1 THEN 
      CASE Col2 
       WHEN @Col2 THEN @curRow := @curRow + 1 
       ELSE @curRow := 1 
      END 
     ELSE @curRow :=1 
    END AS rank, 
    @Col1 := Col1 AS Col1, 
    @Col2 := Col2 AS Col2, 
    Col3, Col4 
    FROM myTable p 
    JOIN (SELECT @curRow := 0, @Col1 := 0, @Col2 := '') r 
    ORDER BY Col1, Col2, Col3 DESC) as tt 
WHERE tt.rank <= 2

替换tt.rank < = 2通过您的期望的索引代替2

回答：

我认为下面代码与预期的一样

declare @tab table (Col1 int, Col2 char(1), Col3 int, Col4 char(1)) 
declare @N int 
insert into @tab 
select 1, 'a' , 2000, 's' 
union all 
select 1 , 'a' , 2002 , 'c' 
union all 
select 1 , 'a' , 2001 , 'b' 
union all 
select 2 , 'b' , 1998 , 's' 
union all 
select 2 , 'b' , 2002 ,'c' 
union all 
select 2 , 'b' , 2000 ,'b' 
union all 
select 3 , 'c' , 2000 ,'b' 
union all 
select 1 , 'f' , 1998 ,'n' 
union all 
select 1 , 'g' , 1999 ,'e' 
;with tab as 
(
select ROW_NUMBER() over(partition by t.col1,t.col2 order by t.col3 desc) as row,t.* 
from @tab t 
) 
select Col1,Col2,Col3,Col4 
from tab 
where row < 3

输出

Col1 Col2 Col3 Col4 
1  a  2002 c 
1  a  2001 b 
1  f  1998 n 
1  g  1999 e 
2  b  2002 c 
2  b  2000 b 
3  c  2000 b

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