Convert sp from MS SQL to MySQL (5.0)

SELECT DISTINCT 
	ComanyID, CompanyName, CompanyURL, ISNULL(School,'') AS School 
FROM (
	SELECT
		T1.ComanyID, T1.CompanyName, T1.CompanyURL, T1.School, T2.DisplayAlways, 
		MAX(T3.SessionEndDate) OVER (PARTITION BY T1.ComanyID) AS DisplayDate
	FROM TrainingCompanies T1
	LEFT JOIN TrainingCourses T2 ON T1.ComanyID = T2.Course_CompanyID
	LEFT JOIN TrainingSessions T3 ON T2.CourseID = T3.Session_CourseID	
	) CompanyListings 
WHERE DisplayDate > DATEADD(D,-3, GETDATE()) OR DisplayAlways = 1
ORDER BY CompanyName 

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Are you certain that your solution is MySQL?  It looks like an MS SQL query.

yes i am
read this : http://dev.mysql.com/doc/refman/5.0/en/from-clause-subqueries.html

Sorry - I don't work with MySQL much & do not know the query syntax very well.  When I cut & pasted the query & ran it (using Navicat) I received the following error:

1064 - You have an error in your SQL syntax... near '') AS School
FROM (
      SELECT

try this

SELECT DISTINCT 
	ComanyID, CompanyName, CompanyURL, IfNULL(School,'') AS School 
FROM (
	SELECT
		T1.ComanyID, T1.CompanyName, T1.CompanyURL, T1.School, T2.DisplayAlways, 
		MAX(T3.SessionEndDate) OVER (PARTITION BY T1.ComanyID) AS DisplayDate
	FROM TrainingCompanies T1
	LEFT JOIN TrainingCourses T2 ON T1.ComanyID = T2.Course_CompanyID
	LEFT JOIN TrainingSessions T3 ON T2.CourseID = T3.Session_CourseID	
	) CompanyListings 
WHERE DisplayDate > DATEADD(D,-3, CURDATE())OR DisplayAlways = 1
ORDER BY CompanyName  

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That solved the initial error - thank you.  

It now stumbles at:
  (PARTITION BY T1.ComanyID) AS DisplayDate
      FROM TrainingCompanies T1

Like I said, I am not familiar with MySQL so it is going to take me some time to go through this.  I will get back to you shortly.

I downloaded a syntax converter (SwissSQL Console) and it gave me an output very similar to what you had which was of limited use as it clearly is not functional MySQL.

Instead of following the example at Xaprb, I re-wrote the query in MS SQL so that it did not use a CTE or 'partition over'.  From that I was able to more easily convert it to MySQL.

      SELECT DISTINCT
                   ComanyID,
                   CompanyName,
                   CompanyURL,
                   COALESCE(School, '') AS School
      FROM TrainingCompanies T1
      LEFT JOIN TrainingCourses T2 ON T1.ComanyID = T2.Course_CompanyID
      WHERE CourseID IN
            (
            SELECT Session_CourseID
            FROM TrainingSessions
            WHERE SessionEndDate > DATE_ADD((CURRENT_TIMESTAMP), INTERVAL  - 3  DAY)
            ) OR DisplayAlways  = 1

ORDER BY CompanyName