SELECT a.*, src.cstat, src.cuser, place1.place1, place2.place2, place3.place3, place4.place4,QC.CategoryName, QC.CategoryId, QOC.CategoryName as OblCategoryName, QOC.CategoryId as OblCategoryId
FROM dzp2r_ariquiz as a
LEFT JOIN dzp2r_ariquizquizcategory QQC ON a.QuizId = QQC.QuizId
LEFT JOIN dzp2r_ariquizcategory QC ON QQC.CategoryId = QC.CategoryId
LEFT JOIN dzp2r_ariquizquizoblcategory QQOC ON a.QuizId = QQOC.QuizId
LEFT JOIN dzp2r_ariquizoblcategory QOC ON QQOC.CategoryId = QOC.CategoryId
LEFT JOIN (SELECT td.quiz_id, count(td.id) as cstat, SUM(td.state_user) as cuser FROM dzp2r_testres_diplom as td WHERE td.quiz_id="3126" GROUP BY td.quiz_id ORDER BY cstat DESC) as src ON src.quiz_id=a.QuizId
LEFT JOIN (SELECT td.quiz_id, count(td.id) as place1 FROM dzp2r_testres_diplom as td WHERE td.quiz_id="3126" AND td.place_name="1" GROUP BY td.quiz_id) as place1 ON place1.quiz_id=a.QuizId
LEFT JOIN (SELECT td.quiz_id, count(td.id) as place2 FROM dzp2r_testres_diplom as td WHERE td.quiz_id="3126" AND td.place_name="2" GROUP BY td.quiz_id) as place2 ON place2.quiz_id=a.QuizId
LEFT JOIN (SELECT td.quiz_id, count(td.id) as place3 FROM dzp2r_testres_diplom as td WHERE td.quiz_id="3126" AND td.place_name="3" GROUP BY td.quiz_id) as place3 ON place3.quiz_id=a.QuizId
LEFT JOIN (SELECT td.quiz_id, count(td.id) as place4 FROM dzp2r_testres_diplom as td WHERE td.quiz_id="3126" AND td.place_type="Лауреат" GROUP BY td.quiz_id) as place4 ON place4.quiz_id=a.QuizId
WHERE a.Status=1 AND a.QuizId=3126
ORDER BY src.cstat DESC

Основы SQL Server