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    <p>The code below shows how to calculate the media of a set of decimal numbers within an SQLAggregate. It resolves the issue of size parameter limitation implementing a data dictionary. The idea is taken from Expert SQL Express 2005.</p> <pre><code>using System; using System.Data; using System.Data.SqlClient; using System.Data.SqlTypes; using Microsoft.SqlServer.Server; using System.Collections.Generic; using System.IO; using System.Linq; using System.Linq.Expressions; using SafeDictionary; [Microsoft.SqlServer.Server.SqlUserDefinedAggregate( Format.UserDefined, MaxByteSize=16)] public struct CMedian2 : IBinarySerialize { readonly static SafeDictionary&lt;Guid , List&lt;String&gt;&gt; theLists = new SafeDictionary&lt;Guid , List&lt;String&gt;&gt;(); private List&lt;String&gt; theStrings; //Make sure to use SqlChars if you use //VS deployment! public SqlString Terminate() { List&lt;Decimal&gt; ld = new List&lt;Decimal&gt;(); foreach(String s in theStrings){ ld.Add(Convert.ToDecimal(s)); } Decimal median; Decimal tmp; int halfIndex; int numberCount; ld.Sort(); Decimal[] allvalues = ld.ToArray(); numberCount = allvalues.Count(); if ((numberCount % 2) == 0) { halfIndex = (numberCount) / 2; tmp = Decimal.Add(allvalues[halfIndex-1], allvalues[halfIndex]); median = Decimal.Divide(tmp,2); } else { halfIndex = (numberCount + 1) / 2; median = allvalues[halfIndex - 1]; tmp = 1; } return new SqlString(Convert.ToString(median)); } public void Init() { theStrings = new List&lt;String&gt;(); } public void Accumulate(SqlString Value) { if (!(Value.IsNull)) theStrings.Add(Value.Value); } public void Merge(CMedian2 Group) { foreach (String theString in Group.theStrings) this.theStrings.Add(theString); } public void Write(System.IO.BinaryWriter w) { Guid g = Guid.NewGuid(); try { //Add the local collection to the static dictionary theLists.Add(g, this.theStrings); //Persist the GUID w.Write(g.ToByteArray()); } catch { //Try to clean up in case of exception if (theLists.ContainsKey(g)) theLists.Remove(g); } } public void Read(System.IO.BinaryReader r) { //Get the GUID from the stream Guid g = new Guid(r.ReadBytes(16)); try { //Grab the collection of strings this.theStrings = theLists[g]; } finally { //Clean up theLists.Remove(g); } } } </code></pre> <p>you also need to implement the dictionary as Expert 2005 does:</p> <pre><code>using System; using System.Collections.Generic; using System.Linq; using System.Text; using System.Threading; namespace SafeDictionary { public class SafeDictionary&lt;K, V&gt; { private readonly Dictionary&lt;K, V&gt; dict = new Dictionary&lt;K,V&gt;(); private readonly ReaderWriterLock theLock = new ReaderWriterLock(); public void Add(K key, V value) { theLock.AcquireWriterLock(2000); try { dict.Add(key, value); } finally { theLock.ReleaseLock(); } } public V this[K key] { get { theLock.AcquireReaderLock(2000); try { return (this.dict[key]); } finally { theLock.ReleaseLock(); } } set { theLock.AcquireWriterLock(2000); try { dict[key] = value; } finally { theLock.ReleaseLock(); } } } public bool Remove(K key) { theLock.AcquireWriterLock(2000); try { return (dict.Remove(key)); } finally { theLock.ReleaseLock(); } } public bool ContainsKey(K key) { theLock.AcquireReaderLock(2000); try { return (dict.ContainsKey(key)); } finally { theLock.ReleaseLock(); } } } } </code></pre> <p>The dictionary must be deployed in a separate assembly with unsafe code grants. The idea is to avoid to serializate all the numbers by keeping in memory data structure dictionary. I recommend the Expert SQL 2005 chapter: </p> <blockquote> <p>CHAPTER 6 ■ SQLCLR: ARCHITECTURE AND DESIGN CONSIDERATIONS.</p> </blockquote> <p>By the way, this solution didn't work for me. Too many conversions from Decimal to String and viceversa make it slow when working with millions of rows, anyway, I enjoyed to try it. For other usages it is a good pattern.</p>
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