Listing 1: C# Code for StringConcat Function
using System;
using System.Data;
using System.Data.SqlClient;
using System.Data.SqlTypes;
using Microsoft.SqlServer.Server;
using System.Text;
using System.IO;
using System.Runtime.InteropServices;

[Serializable]
[SqlUserDefinedAggregate(
 Format.UserDefined,    // user-defined serialization
 IsInvariantToDuplicates = false, // duplicates matter
 IsInvariantToNulls = true,    // don't care about NULLs
  IsInvariantToOrder = false,   // order matters (ignored)
  IsNullIfEmpty = false,      // don't yield NULL if empty set
  MaxByteSize = 8000)]       // maximum size in bytes
public struct StringConcat : IBinarySerialize
{
  private StringBuilder sb;

  public void Init()
  {
    this.sb = new StringBuilder();
  }

  public void Accumulate(SqlString s)
  {
    if (s.IsNull)
    {
      return;         // skip NULLs
    }
    else
    {
      this.sb.Append(s.Value);
    }
  }

  public void Merge(StringConcat Group)
  {
    this.sb.Append(Group.sb);
  }

  public SqlString Terminate()
  {
    return new SqlString(this.sb.ToString());
  }

  public void Read(BinaryReader r)
  {
    sb = new StringBuilder(r.ReadString());
  }

  public void Write(BinaryWriter w)
  {
    if (this.sb.Length > 4000) // limit sb to 8000 bytes
      w.Write(this.sb.ToString().Substring(0, 4000));
    else
      w.Write(this.sb.ToString());
  }

}  // end StringConcat