IF (SELECT CHARACTER_MAXIMUM_LENGTH FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME = 'MY_TABLE' AND COLUMN_NAME = 'MY_COLUMN')<>-1
BEGIN
	ALTER TABLE [dbo].[MY_TABLE] ALTER COLUMN [MY_COLUMN] [nvarchar](max) NOT NULL
END

This code checks length of the field which is specific number for standard NVARCHAR and -1 for NVARCHAR(max), and alters column type only if it hasn't already been altered.

if not (exists(SELECT * FROM SYSCOLUMNS WHERE ID = OBJECT_ID('[dbo].[MY_TABLE]') AND Name = 'NEW_COLUMN'))
BEGIN
	ALTER TABLE [dbo].[MY_TABLE] ADD [NEW_COLUMN] [int] NULL
	UPDATE [dbo].[MY_TABLE] SET [NEW_COLUMN] = 1
END

But this doesn't work - you get "Invalid column name" error. The trick is - you don't need a separate UPDATE statement. ALTER TABLE ... ADD statement has a DEFAULT parameter. You can modify previous code like this:

if not (exists(SELECT * FROM SYSCOLUMNS WHERE ID = OBJECT_ID('[dbo].[MY_TABLE]') AND Name = 'NEW_COLUMN'))
BEGIN
	ALTER TABLE [dbo].[MY_TABLE] ADD [NEW_COLUMN] [int] NULL DEFAULT 1 WITH VALUES
END

This ALTER statement assigns default value of 1 to the new column. WITH VALUES parameter is important, it populates existing rows with the default value (without it it will be populated by NULLs).

I was looking for a WordPress plugin that would allow me to mass-delete empty posts, but apparently none exist. You can delete posts based on date, tags, category, but not the content. Fortunately if you have access to phpMyAdmin of your MySQL installation - there is a solution.

Warning! Backup your database before performing following operations!

In phpMyAdmin locate the database that hosts your blog data. In a standard WordPress installation table "wp_posts" holds all blog's posts. In case of WordPress MU the table name would be "wp_<blog_number>_posts", for example "wp_6_posts". The content of the post in both cases is stored in "post_content" field. So to delete all empty posts in a standard WordPress following SQL query can be used:

DELETE FROM wp_posts WHERE post_content=''

To delete blank posts for a specific blog in a WordPress MU installation, query similar to this one can be used:

DELETE FROM wp_6_posts WHERE post_content=''

This example assumes you're working with blog #6.

SELECT ContactName, Country FROM Customers ORDER BY Country

on Northwind database and getting following result:

ContactName           Country
Patricio Simpson      Argentina
Yvonne Moncada        Argentina
Sergio Gutiérrez      Argentina
Georg Pipps           Austria
Roland Mendel         Austria
Catherine Dewey       Belgium
Pascale Cartrain      Belgium
Anabela Domingues     Brazil
Paula Parente         Brazil
Bernardo Batista      Brazil
Lúcia Carvalho        Brazil
Janete Limeira        Brazil
Aria Cruz             Brazil
André Fonseca         Brazil
Mario Pontes          Brazil
Pedro Afonso          Brazil
Elizabeth Lincoln     Canada
Jean Fresnière        Canada
Yoshi Tannamuri       Canada
...

You're asked to retreive only the 2nd and the 5th group of contacts. How do you do it? DENSE_RANK() is the answer. Modify the query like this:

SELECT ContactName, Country, DENSE_RANK() OVER (ORDER BY Country) FROM Customers

The DENSE_RANK() function returns rank (number) of row group where partition is specified in OVER(ORDER BY...) clause. Here is the result:

ContactName           Country            No column name
Patricio Simpson      Argentina          1
Yvonne Moncada        Argentina          1
Sergio Gutiérrez      Argentina          1
Georg Pipps           Austria            2
Roland Mendel         Austria            2
Catherine Dewey       Belgium            3
Pascale Cartrain      Belgium            3
Anabela Domingues     Brazil             4
Paula Parente         Brazil             4
Bernardo Batista      Brazil             4
Lúcia Carvalho        Brazil             4
Janete Limeira        Brazil             4
Aria Cruz	          Brazil             4
André Fonseca         Brazil             4
Mario Pontes          Brazil             4
Pedro Afonso          Brazil             4
Elizabeth Lincoln     Canada             5
Jean Fresnière        Canada             5
Yoshi Tannamuri       Canada             5
...

Now the only thing left is to select group with rank 2 and 5:

SELECT ContactName, Country FROM
 (SELECT ContactName, Country, DENSE_RANK() OVER (ORDER BY Country) AS GROUP_NO
  FROM Customers) AS Cust
WHERE GROUP_NO IN (2,5)

The result:

ContactName           Country
Georg Pipps           Austria
Roland Mendel         Austria
Elizabeth Lincoln     Canada
Jean Fresnière        Canada
Yoshi Tannamuri       Canada

Consider Employees table of the Northwind database. When I run following query:

SELECT Country, FirstName FROM Employees ORDER BY Country, FirstName

I get following result:

Country FirstName
UK      Anne
UK      Michael
UK      Robert
UK      Steven
USA     Andrew
USA     Janet
USA     Laura
USA     Margaret
USA     Nancy

Now I want to combine first names into comma separated strings grouped by country.Take a look at following SQL code:

SELECT DISTINCT Country,

(STUFF((SELECT ',' + FirstName FROM Employees E2 WHERE  E1.Country = E2.Country	ORDER BY FirstName
FOR XML PATH(''), TYPE, ROOT).value('root[1]','nvarchar(max)'),1,1,'')) as FirstNames

FROM Employees E1 ORDER BY Country

The internal subquery is the important part. The FOR XML PATH clause combines data into a single output, the ,TYPE, ROOT statements make sure that the output is of XML type with a root node. And the .value method converts output into varchar to display characters like "<" or ">" correctly. The result:

Country  FirstNames
UK       Anne,Michael,Robert,Steven
USA      Andrew,Janet,Laura,Margaret,Nancy

Function GroupBy(ByVal i_sGroupByColumn As String, ByVal i_sAggregateColumn As String, ByVal i_dSourceTable As DataTable) As DataTable

        'getting distinct values for group column
        Dim dv As New DataView(i_dSourceTable)

        'adding column for the row count
        Dim dtGroup As DataTable = dv.ToTable(True, New String() {i_sGroupByColumn}) 

        dtGroup.Columns.Add("Count", GetType(Integer)) 

        'looping thru distinct values for the group, counting
        For Each dr As DataRow In dtGroup.Rows
            dr("Count") = i_dSourceTable.Compute("Count(" & i_sAggregateColumn & ")", i_sGroupByColumn & " = '" & dr(i_sGroupByColumn) & "'")
        Next        

        'returning grouped/counted result
        Return dtGroup
End Function

The function first gets distinct values for group-by column, by creating a data view from source data table and using DataView’s "ToTable" method. It then loops thru these distinct values performing aggregate function on the source table using DataTable’s "Compute" method - Count in this case, but it can easily be replaced with other aggregates.

An excellent article at SQL Hacks suggest adding "e0" to the data when passing it to IsNumeric function. What it does essentualy is making the number to be in scientific format, e.g 12.34 becomes 12.34e0 (or 12.34 * 1). Which still remains a number. So IsNumeric(12.34e0) returns 1 while IsNumeric($e0) returns 0.

Which works great until actual number in scientific format is passed.  If you try to test for example 1.234e5, IsNumeric correctly returns 1, but by adding "e0" as article suggest IsNumeric(1.2345e5e0) returns 0.

To work around this limitation I simple test for an "e" within passed data. If it exist, I am calling IsNumeric as usual, if it does not - I am adding "e0" to the tested data:

CREATE FUNCTION IsRealNumber (@i_sValueToTest nvarchar(250))
/* This function tests if passed in value a real number */

RETURNS int
AS
BEGIN
       DECLARE @iResult int

      -- if there is 'E' in the value - do a standard IsNumeric test
     IF CHARINDEX('E', UPPER(@i_sValueToTest))<> 0
            SET @iResult = IsNumeric(@i_sValueToTest)
      -- Otherwise do a modified IsNumeric test by adding 'E0' at the end
    ELSE
          SET @iResult = IsNumeric(@i_sValueToTest + 'E0')

        RETURN @iResult
END