Optimizing SQL Server Clustered Indexes

When deciding on whether to create a clustered or non-clustered index, it is often helpful to know what the estimated size of the clustered index will be. Sometimes, the size of a clustered index on a particular column or columns may be very large, leading to database size bloat and increased disk I/O. 

Clustered index values often repeat many times in a table's non-clustered storage structures, and a large clustered index value can unnecessarily increase the physical size of a non-clustered index. This increases disk I/O and reduces performance when non-clustered indexes are accessed.

Because of this, ideally a clustered index should be based on a single column (not multiple columns) that is as narrow as possible. This not only reduces the clustered index's physical size, it also reduces the physical size of non-clustered indexes and boosts SQL Servers overall performance.

When you create a clustered index, try to create it as a UNIQUE clustered index, not a non-unique clustered index. The reason for this is that while SQL Server will allow you to create a non-unique clustered index, under the surface, SQL Server will make it unique for you by adding a 4-byte "uniqueifer" to the index key to guarantee uniqueness. This only serves to increase the size of the key, which increases disk I/O, which reduces performance. If you specify that your clustered index is UNIQUE when it is created, you will prevent this unnecessary overhead.

Happy query....

A little missunderstood in GROUP BY ln SQL SERVER

for example i tried to view how much news posted grouping by week in year 2009

     SELECT 
        DATEPART(WK,DatePosted) AS WeekNumber, 
        COUNT(NewsID) AS NewsPosts
     FROM News
     WHERE DATEPART(YYYY, dbo.News.DatePosted) = 2009
     ORDER BY WeekNumber

you will get the warning message

error , Line 5
Column 'News.DatePosted' is invalid in the select list because it is not contained in either an aggregate function or the GROUP BY clause.

what's wrong? yup you need to add the group by
so we are going to add the group by

    SELECT
        DATEPART(WK,DatePosted) AS WeekNumber,
        COUNT(NewsID) AS NewsPosts
    FROM News
    WHERE DATEPART(YYYY, dbo.News.DatePosted) = 2009
    GROUP BY WeekNumber
    ORDER BY WeekNumber

still error? try to use the column instead, it's because sql server group by only regonise the column in group by not alias (like in My SQL)

Get list of Ms Access Table

Sub ListAccessTables2(strDBPath)
   Dim cnnDB As ADODB.Connection
   Dim rstList As ADODB.Recordset

   Set cnnDB = New ADODB.Connection

   ' Open the connection.
   With cnnDB
      .Provider = "Microsoft.Jet.OLEDB.4.0"
      .Open strDBPath
   End With

   ' Open the tables schema rowset.
   Set rstList = cnnDB.OpenSchema(adSchemaTables)

   ' Loop through the results and print the
   ' names and types in the Immediate pane.
   With rstList
      Do While Not .EOF
         If .Fields("TABLE_TYPE") <> "VIEW" Then
            Debug.Print .Fields("TABLE_NAME") & vbTab & _
               .Fields("TABLE_TYPE")
         End If
         .MoveNext
      Loop
   End With
   cnnDB.Close
   Set cnnDB = Nothing
End Sub