SQL CLR Aggregate: Median

Since Sql Server doesn't have an aggregate for Median, I figured, that I'll create my first SQL CLR to handle this problem.

So, I created my intial project, using the .Net Framework 3.5 and C# SQL CLR aggregate template, and started coding:

Code Snippet

using System;
using System.Data;
using System.Data.SqlClient;
using System.Data.SqlTypes;
using Microsoft.SqlServer.Server;
using System.Collections.Generic;


[Serializable]
[Microsoft.SqlServer.Server.SqlUserDefinedAggregate(
    Format.UserDefined,
    IsInvariantToDuplicates = false,
    IsInvariantToNulls = false,
    IsInvariantToOrder = false,
    MaxByteSize = 8000)]
public struct Median : IBinarySerialize
{
    //Variables to hold the values;
    private List<double> ld;

    public void Init()
    {
        ld = new List<double>();
    }

    public void Accumulate(SqlDouble Value)
    {
        if (!Value.IsNull)
        {
            ld.Add(Value.Value);
        }
    }

    ///

    /// Merge the partially computed aggregate with this aggregate.
    ///
    /// The other partial results to be merged
    public void Merge(Median Group)
    {
        this.ld.AddRange(Group.ld.ToArray());
    }

    ///

    /// Called at the end of aggregation, to return the results.
    ///
    /// The median of all inputted values
    public SqlDouble Terminate()
    {
        //debug: return (SqlDouble)ld.Count;

        //special case 0 values
        if (ld.Count == 0)
            return SqlDouble.Null;

        ld.Sort();
        int index = (int)ld.Count / 2;

        if (ld.Count % 2 == 0)
        {
            return (SqlDouble)(((double)ld[index] + (double)ld[index - 1]) / 2);
        }
        else
        {
            return (SqlDouble)((double)ld[index]);
        }
    }


    #region IBinarySerialize Members

    public void Read(System.IO.BinaryReader r)
    {
        int cnt = r.ReadInt32();
        this.ld = new List<double>(cnt);
        for(int i = 0; i < cnt; i++)
        {
            this.ld.Add(r.ReadDouble());
        }
    }

    public void Write(System.IO.BinaryWriter w)
    {
        w.Write(this.ld.Count);
        foreach (double d in this.ld)
        {
            w.Write(d);
        }
    }

    #endregion
}

Some of the intial changes that I've made from the default:
1) The SqlUserDefinedAggregate default was Format.Native. The problem with using the default Serializer is that I needed a way to store my values, preferably in a List. By changing the format to Format.UserDefined  -- I was able to create my own serializer. In this case I used the IBinarySerialize interface.

2) I also changed the default IsInvariant attributes.

• IsInvariantToDuplicates - set to false since I want duplicates.
• IsInvariantToNull - set to false since I will handle Null values in my code.
• IsInvariantToOrder - set to false, I can do this in code.

Once the code is compiled, you will need to place the dll on the same machine as the SQL Server is located.

Using the following query to set the assembly and aggregate name:

Code Snippet

IF EXISTS (SELECT name FROM sysobjects WHERE name = 'Median')
   DROP AGGREGATE Median
go

IF EXISTS (SELECT name FROM sys.assemblies WHERE name = 'MyClrCode')
   DROP ASSEMBLY MyClrCode
go


CREATE ASSEMBLY MyClrCode
FROM 'C:\Median.dll'
WITH PERMISSION_SET = SAFE
GO

CREATE AGGREGATE dbo.Median
(@input float)
RETURNS float
EXTERNAL NAME MyClrCode.Median

Once done, time to do some testing. An example:

Code Snippet

--Test 1 value
select
dbo.Median(x.y)
from
(
    select 1 as y
)x
GO

--Test Accuracy
select
dbo.Median(x.y)
from
(
    select 1 as y
    union all
    select 2 as y
)x
GO

SSRS: Saving User Settings from the Report

Sometimes, different report's parameters default values are needed for each users. Here is a way, each user can save their default settings for the next time they run an SSRS report, from the report itself.

We will need to save the user's settings to a database table.
Table create query:

SETQUOTED_IDENTIFIER ON
GO

SETANSI_PADDING ON
GO

CREATETABLE [dbo].[UserSettings](
[UserSettingSQN] [int] IDENTITY(1,1) NOT NULL,
[UserID] [varchar] (50) NOT NULL,
[ReportName] [varchar] (50) NOT NULL,
[ParameterName] [varchar](50) NULL,[ParameterValue] [varchar](max) NULL,
[LastUpdateDate] [datetime] NOT NULL,
CONSTRAINT [PK_UserSettingSQN] PRIMARY KEY CLUSTERED
(   [UserSettingSQN] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY],
CONSTRAINT [IX_UserSettings] UNIQUE NONCLUSTERED
([UserID] ASC,
[ReportName] ASC,
[ParameterName] ASC
)WITH (PAD_INDEX = OFF, STATISTICS_NORECOMPUTE = OFF, IGNORE_DUP_KEY = OFF, ALLOW_ROW_LOCKS = ON, ALLOW_PAGE_LOCKS = ON) ON [PRIMARY]
)ON [PRIMARY]
GO
SETANSI_PADDING OFF
GO

The fields:

• UserID: to store the user info that they used to access the report. I currently store both the computer and username.
• ReportName: The name of the report
• ParameterName: Parameter that is used in the report that is to be saved.
• ParameterValue: Value the user set to save.

An example of the data:

 The Report:

In the Reports, I've created 3 additional parameters, to be used for saving the user's default parameter settings:

• UserID: I use the SSRS's built-in field, User!UserID, to get the ID of the user running the report. Set the visibility to be internal.
• ReportName: Again, I use the SSRS's built-in field, Globals!ReportName, to get the name of the report as it is stored on the report server database. Set the visibility to be internal.
• Save: A boolean field that is visible to the user. I have the default set to "False", so when the user wants to change his/her settings they can change it to true when they run the report.

So when they run the report, I have the stored procedure check to see if the boolean was set to 1 -- if so then save with update/insert.

IF@Save = 1
BEGIN
UPDATE [ScientificArray].dbo.UserSettings WITH (SERIALIZABLE) SET ParameterValue = @StringNames
WHERE UserID = @UserID AND ReportName = @ReportName AND ParameterName = 'InverterString'
IF @@ROWCOUNT = 0
BEGIN
INSERT INTO [ScientificArray].dbo.UserSettings (UserID, ReportName, ParameterName, ParameterValue, LastUpdateDate) VALUES (@UserID, @ReportName, 'InverterString', @StringNames, GETDATE())
END
END

Removing accents for string comparisons in tsql

I've been reading The Daily WTF, and found this one interesting: http://thedailywtf.com/Articles/The-AntiSQL-Coalition-.aspx

By using the Latin1_General_CI_AI   (AI stands for Accent Insensitive)
the user was able to by-pass special characters like: É,È,Ê, and Ë for E when doing a search.
Example:

SELECT*
FROMPersons
WHEREname collate Latin1_General_CI_AI LIKE @name
AND surname collate Latin1_General_CI_AI LIKE @surname
ORDERBY name, surname

Additional references:
http://msdn.microsoft.com/en-us/library/ms187582.aspx


P.S. Funny to see other companies have Database haters too.