在SQL中选择2列的不同组合

Question

当我在我的表上有多个连接后运行一个select时,我有一个2列的输出,我想为返回的行集选择col1和col2的不同组合.

我运行的查询将是这样的:

select a.Col1,b.Col2 from a inner join b on b.Col4=a.Col3

现在输出有点像这样

Col1 Col2  
1   z  
2   z  
2   x  
2   y  
3   x  
3   x  
3   y  
4   a  
4   b  
5   b  
5   b  
6   c  
6   c  
6   d  

现在我想输出应该是如下

1  z  
2  y  
3  x  
4  a  
5  b  
6  d 

如果我随机选择第二列就可以了,因为我的查询输出就像一百万行而且我真的认为有一种情况我会让Col1和Col2输出相同,即使这是我可以编辑的值..

你可以帮我一样吗...我认为基本上col3需要是一个行号我猜,然后我需要在随机行号上选择两个cols基础..我不知道如何将它转换为SQL

考虑案例1a 1b 1c 1d 1e 2a 2b 2c 2d 2e现在group by将给出我所有这些结果,因为我想要1a和2d或1a和2b.任何这样的组合.

好吧,让我解释一下我的期望:

with rs as(
select a.Col1,b.Col2,rownumber() as rowNumber from a inner join b on b.Col4=a.Col3)
select rs.Col1,rs.Col2 from rs where rs.rowNumber=Round( Rand() *100)

现在我不知道如何让rownumber或随机正常工作!

提前致谢.

Answer 1

如果你根本不在乎col2返回什么值

select a.Col1,MAX(b.Col2) AS Col2
from a inner join b on b.Col4=a.Col3 
GROUP BY a.Col1

如果您确实需要随机值,可以使用以下方法.

 ;WITH T
     AS (SELECT a.Col1,
                b.Col2
                ROW_NUMBER() OVER (PARTITION BY a.Col1 ORDER BY (SELECT NEWID())
                ) AS RN
         FROM   a
                INNER JOIN b
                  ON b.Col4 = a.Col3)
SELECT Col1,
       Col2
FROM   T
WHERE  RN = 1  

或者使用CLR聚合函数.这种方法的优点在于它消除了通过partition, newid()下面的示例实现进行排序的要求.

using System;
using System.Data.SqlTypes;
using System.IO;
using System.Security.Cryptography;
using Microsoft.SqlServer.Server;

[Serializable]
[SqlUserDefinedAggregate(Format.UserDefined, MaxByteSize = 8000)]
public struct Random : IBinarySerialize
{
    private MaxSoFar _maxSoFar;

    public void Init()
    {
    }

    public void Accumulate(SqlString value)
    {
        int rnd = GetRandom();
        if (!_maxSoFar.Initialised || (rnd > _maxSoFar.Rand))
            _maxSoFar = new MaxSoFar(value, rnd) {Rand = rnd, Value = value};
    }

    public void Merge(Random group)
    {
        if (_maxSoFar.Rand > group._maxSoFar.Rand)
        {
            _maxSoFar = group._maxSoFar;
        }
    }

    private static int GetRandom()
    {
        var buffer = new byte[4];

        new RNGCryptoServiceProvider().GetBytes(buffer);
        return BitConverter.ToInt32(buffer, 0);
    }

    public SqlString Terminate()
    {
        return _maxSoFar.Value;
    }

    #region Nested type: MaxSoFar

    private struct MaxSoFar
    {
        private SqlString _value;

        public MaxSoFar(SqlString value, int rand) : this()
        {
            Value = value;
            Rand = rand;
            Initialised = true;
        }

        public SqlString Value
        {
            get { return _value; }
            set
            {
                _value = value;
                IsNull = value.IsNull;
            }
        }

        public int Rand { get; set; }

        public bool Initialised { get; set; }
        public bool IsNull { get; set; }
    }

    #endregion


    #region IBinarySerialize Members

    public void Read(BinaryReader r)
    {
        _maxSoFar.Rand = r.ReadInt32();
        _maxSoFar.Initialised = r.ReadBoolean();
        _maxSoFar.IsNull = r.ReadBoolean();

        if (_maxSoFar.Initialised && !_maxSoFar.IsNull)
            _maxSoFar.Value = r.ReadString();
    }

    public void Write(BinaryWriter w)
    {
        w.Write(_maxSoFar.Rand);
        w.Write(_maxSoFar.Initialised);
        w.Write(_maxSoFar.IsNull);

        if (!_maxSoFar.IsNull)
            w.Write(_maxSoFar.Value.Value);
    }

    #endregion
}