Jak wygenerować to zapytanie SQL, takie jak tabela przestawna

Możesz to zrobić za pomocą CASE oświadczenie:

SELECT p.productid, p.da, p.ig, p.des
      ,GROUP_CONCAT(CASE WHEN ck.title = 'St Code' 
                         THEN cv.value ELSE NULL END) AS 'St Code'
      ,GROUP_CONCAT(CASE WHEN ck.title = 'Rear Les' 
                         THEN cv.value ELSE NULL END) AS 'Rear Les'
FROM Products p
JOIN code_values cv ON p.productid = cv.pid
JOIN code_keys ck ON cv.codeid = ck.codeid
GROUP BY p.productid;

Jeśli masz nieznaną liczbę code_keys możesz wypróbować to dynamiczne zapytanie:

SET @sql = NULL;
SELECT
  GROUP_CONCAT(DISTINCT
    CONCAT(
      'GROUP_CONCAT(CASE WHEN `title` = ''',
      `title`,
      ''' THEN cv.value ELSE NULL END) AS `',
      `title`, '`'
    )
  ) INTO @sql
FROM code_keys ck JOIN code_values cv ON cv.codeid = ck.codeid;

SET @sql = CONCAT('SELECT p.productid, p.da, p.ig, p.des, ', @sql,'
                     FROM Products p
                     JOIN code_values cv ON p.productid = cv.pid
                     JOIN code_keys ck ON cv.codeid = ck.codeid
                    GROUP BY p.productid
                  ');

PREPARE stmt FROM @sql;
EXECUTE stmt;
DEALLOCATE PREPARE stmt;

Wyjście:

| PRODUCTID | DA | IG | DES |      ST CODE |  REAR LES |
--------------------------------------------------------
|         5 | 78 | 33 |  23 | ST 102 200 R | 12 000 33 |
|         8 | 88 | 13 |  21 | ST 100 101 R | 11 223 34 |

Zobacz ten SQLFiddle