Mysql – How to apply transpose method in MYSQL, Getting rows as collumns

Firstly, I think your original query may not be "correct"; With reference to your SQLFiddle, it looks to me as though you should be returning rows with ID = 2, 3 and 4 (in addition to the row with ID = 1 you are getting from this half), because your existing logic appears as though you intended for these other rows to be included, as they explicitly meet the OR (date_from >= '2014-04-10 08:00:00') part of your second WHERE clause.

The GROUP BY teacher_id clause in your second part of your UNION is causing you to lose those rows. This is because you're not actually aggregating any columns in your select list, and in this case the GROUP BY will cause 'difficult to define' behaviour.

Also, while I can't explain the poor performance of your UNION, I can work around it for you by outright removing it from your query:

Rather than using two separate (and in parts, repeating) sets of logic to get rows from the same table, I've consolidated your logic into one query with the differences in your logic ORed together - ie if a row meets one or the other of your original WHERE clauses, it's included. This is possible because I've replaced the (INNER) JOIN you were using to find the closestDate with a LEFT JOIN.

This LEFT JOIN means we are now also able to distinguish which set of logic should be applied to a row; If the join works (closestDate IS NOT NULL) we apply your logic from the first half, but if the join fails (closestDate IS NULL) then we apply the logic from your second half.

So this will return all the rows that your query returned (in the fiddle), and it's also picking up those additional ones.

  SELECT
    *

  FROM 
    teacher_slots ts

    LEFT JOIN 
    (
      SELECT 
        teacher_id,
        DATE(MIN(date_from)) as closestDay

      FROM 
        teacher_slots

      WHERE   
        date_from >= '2014-04-10 08:00:00' 
        AND order_of_arrival = 0
        AND status = 0 
        AND city_id = 6015 
        AND subject_id = 1

      GROUP BY 
        teacher_id

    ) a
    ON a.teacher_id = ts.teacher_id
    AND a.closestDay = DATE(ts.date_from)

  WHERE 
    /* conditions that were common to both halves of the union */
    ts.status = 0
    AND ts.city_id = 6015
    AND ts.subject_id = 1

    AND
    (
      (
        /* conditions that were from above the union 
           (ie when we joined to get closest future date) */
        a.teacher_id IS NOT NULL
        AND ts.date_from >= '2014-04-10 08:00:00'
        AND ts.order_of_arrival = 0
      ) 
      OR
      (
        /* conditions that were below the union 
          (ie when we didn't join) */
        a.teacher_id IS NULL       
        AND ts.order_of_arrival = 1 
        AND 
        (
          (
            date_from <= '2014-04-10 08:00:00' 
            AND  
            date_to >= '2014-04-10 08:00:00'
          )

          /* rows that met this condition were being discarded 
             as a result of 'difficult to define' GROUP BY behaviour. */
          OR date_from >= '2014-04-10 08:00:00' 
        )
      )
    )

  ORDER BY 
   ts.date_from ASC;

Further, you can "tidy up" your query further so that you don't need to "plug in" your status, city_id and subject_id parameters more than once.

To do this, change the subquery a to also select those columns, and to also group on those columns. Then, the JOIN's ON clause would need to map those columns to their ts.xxx equivalents.

I don't think this will negatively effect performance, but couldn't be sure without testing on a large dataset.

So your join will look more like:

LEFT JOIN 
(
  SELECT 
    teacher_id,
    status,
    city_id,
    subject_id,
    DATE(MIN(date_from)) as closestDay

  FROM 
    teacher_slots

  WHERE   
    date_from >= '2014-04-10 08:00:00' 
    AND order_of_arrival = 0
  /* These no longer required here...
    AND status = 0 
    AND city_id = 6015 
    AND subject_id = 1
  */

  GROUP BY 
    teacher_id,
    status,
    city_id,
    subject_id

) a
ON a.teacher_id = ts.teacher_id
AND a.status = ts.status 
AND a.city_id = ts.city_id 
AND a.subject_id = ts.city_id
AND a.closestDay = DATE(ts.date_from)

It seems you want a triangular self-join. Just change the <> to <:

AND p1.ProductID < p2.ProductID

You also do not need the copy table Product2. You can join the table to itself. See SQL-Fiddle:

INSERT INTO VariationJoin
SELECT 
    p1.ProductID as ProductID1,
    p2.ProductID as ProductID2, 
    p1.Title, p1.SubTitle, p1.SubSubTitle
FROM Product1 p1                              -- same table
  INNER JOIN Product1 p2                      -- different alias
    ON  p1.Title = p2.Title 
    AND p1.SubTitle = p2.SubTitle 
    AND p1.SubSubTitle = p2.SubSubTitle 
    AND p1.ProductID < p2.ProductID ;