SQLCLR custom aggregate with multiple sql_variant parameters

Question

Hy,

I have post a question about CLR User-Defined Aggregates few month ago oon this post.

This works like a charm. But now I would like to quite the same functions with the two parameters in sql_variant type.

Like in my previous post, the two function would be sMax and sMin and will return the first value depending on the second.

I found that the sql_variant type is a object type in C#. But I having difficulties to accumulate and compare the object.

What is the best option to compare this two object without knowing the type?

Answer 1

When using SQL_VARIANT / object, you can determine the type by using the GetType() method as follows:

[Microsoft.SqlServer.Server.SqlFunction(IsDeterministic = false, IsPrecise = true)]
public static SqlBoolean GetIfSmallInt(object SomeValue)
{
    return (SomeValue.GetType() == typeof(SqlInt16));
}

And test it using:

DECLARE @DateTime DATETIME = GETDATE();
SELECT dbo.GetIfSmallInt(@DateTime);
-- 0

DECLARE @SmallInt SMALLINT = 5;
SELECT dbo.GetIfSmallInt(@SmallInt);
-- 1

Please keep in mind that using SQL_VARIANT / object has a noticeable performance penalty. Only use it when you absolutely need to. If you just need to pass in INT / SMALLINT / BIGINT, then use BIGINT / SqlInt64 as the input parameter type.

Answer 2

Thanks for your response. I use this philosophy to complete my aggregate function.

So far, it's working but not everythinks fine...

• the isNull not working
• without the isNull, using the Convert.ToString is not good, it replace null value by empty string. But without it crash with empty values
• in the Read function : use the ReadString function. ReadBytes is better?
• To perform the CompareTo, using the Convert and the toString, is it the good approach ?

The code :

using System;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Data.SqlTypes;
using System.Diagnostics.Eventing.Reader;
using System.Globalization;
using Microsoft.SqlServer.Server;
using System.Text;
using System.Collections;
using System.IO;

[Serializable]
[SqlUserDefinedAggregate(
    Format.UserDefined,
    IsInvariantToOrder = true,
    IsInvariantToNulls = true,
    IsInvariantToDuplicates = true,
    MaxByteSize = -1)]
public struct sMax : IBinarySerialize, INullable
{
    #region Helpers

    private struct MyData
    {
        public object Data { get; set; }
        public InType DataType { get; set; }

        public object Group { get; set; }
        public InType GroupType { get; set; }

        public int CompareTo(MyData other)
        {
            if (Group == null)
                return other.Group == null ? 0 : -1;

            if (other.Group == null)
                return 1;

            if (GroupType == InType.Int)
                return Convert.ToInt32(Group).CompareTo(Convert.ToInt32(other.Group));
            if (GroupType == InType.BigInt)
                return Convert.ToInt64(Group).CompareTo(Convert.ToInt64(other.Group));
            if (GroupType == InType.Double)
                return Convert.ToDouble(Group).CompareTo(Convert.ToDouble(other.Group));
            if (GroupType == InType.Date)
                return Convert.ToDateTime(Group.ToString()).CompareTo(Convert.ToDateTime(other.Group.ToString()));
            if (GroupType == InType.String)
                return Convert.ToString(Group).CompareTo(Convert.ToString(other.Group));
            else
                return 0;
        }

        public static bool operator < (MyData left, MyData right)
        {
            return left.CompareTo(right) == -1;
        }

        public static bool operator > (MyData left, MyData right)
        {
            return left.CompareTo(right) == 1;
        }
    }

    private enum InType
    {
        String,
        Int,
        BigInt,
        Date,
        Double,
        Unknow
    }

    private InType GetType(object value)
    {
        if (value.GetType() == typeof(SqlInt32))
            return InType.Int;
        else if (value.GetType() == typeof(SqlInt64))
            return InType.BigInt;
        else if (value.GetType() == typeof(SqlString))
            return InType.String;
        else if (value.GetType() == typeof(SqlDateTime))
            return InType.Date;
        else if (value.GetType() == typeof(SqlDouble))
            return InType.Double;
        else
            return InType.Unknow;
    }

    #endregion

    private MyData _maxItem;

    public void Init()
    {
        _maxItem = default(MyData);

        this.IsNull = true;
    }

    public void Accumulate(object data, object group)
    {
        if (data != null && group != null)
        {
            var current = new MyData
            {
                Data = data,
                Group = group,
                DataType = GetType(data),
                GroupType = GetType(group)
            };

            if (current > _maxItem)
            {
                _maxItem = current;
            }
        }
    }

    public void Merge(sMax other)
    {
        if (other._maxItem > _maxItem)
        {
            _maxItem = other._maxItem;
        }
    }

    public SqlString Terminate()
    {
        return this.IsNull ? SqlString.Null : new SqlString(_maxItem.Data.ToString());
    }

    public void Read(BinaryReader reader)
    {
        IsNull = reader.ReadBoolean();
        _maxItem.Group = reader.ReadString();
        _maxItem.Data = reader.ReadString();

        if (_maxItem.Data != null)
            this.IsNull = false;
    }

    public void Write(BinaryWriter writer)
    {
        writer.Write(this.IsNull);
        writer.Write(_maxItem.Group.ToString());
        writer.Write(_maxItem.Data.ToString());
    }

    public Boolean IsNull { get; private set; }
}