mysql се присъединява към същата таблица с различен набор от резултати

Изглежда, че това е, което искате. Актуализирах първата заявка, за да използвам правилния ANSI JOIN синтаксис и след това за допълнителните две заявки те бяха обединени чрез LEFT JOIN на stats_host поле:

SELECT s.stats_host,
  h.host_name,
  s.stats_avgcpu,
  s.stats_avgmem,
  s.stats_avgswap,
  s.stats_avgiowait,
  s7.7dayavgcpu,
  s7.7dayavgmem,
  s7.7dayavgswap,
  s7.7dayavgiowait,
  s30.30dayavgcpu,
  s30.30dayavgmem,
  s30.30dayavgswap,
  s30.30dayavgiowait
FROM sar_stats s
INNER JOIN sar_hosts h
  on s.stats_host = h.host_id
INNER JOIN sar_appgroups a
  on h.host_appgroup = a.group_id
  and a.group_name = 'Pervasive'
INNER JOIN sar_environments e
  on h.host_environment = e.env_id
  and e.env_name = 'Staging 2'
LEFT JOIN
(
  SELECT s.stats_host,
    AVG(s.stats_avgcpu) AS '7dayavgcpu',
    AVG(s.stats_avgmem) AS '7dayavgmem',
    AVG(s.stats_avgswap) AS '7dayavgswap',
    AVG(s.stats_avgiowait) AS '7dayavgiowait'
  FROM sar_stats s
  WHERE DATE(stats_report_time) BETWEEN DATE_SUB(curdate(), INTERVAL 8 DAY) AND DATE_SUB(curdate(), INTERVAL 1 DAY)
  GROUP BY s.stats_host
) s7
  on s.stats_host = s7.stats_host
LEFT JOIN
(
  SELECT s.stats_host,
    AVG(s.stats_avgcpu) AS '30dayavgcpu',
    AVG(s.stats_avgmem) AS '30dayavgmem',
    AVG(s.stats_avgswap) AS '30dayavgswap',
    AVG(s.stats_avgiowait) AS '30dayavgiowait'
  FROM sar_stats s
  WHERE DATE(s.stats_report_time) BETWEEN DATE_SUB(curdate(), INTERVAL 31 DAY) AND DATE_SUB(curdate(), INTERVAL 1 DAY)
  GROUP BY s.stats_host
) s30
  on s.stats_host = s30.stats_host
WHERE DATE(s.stats_report_time) =  DATE_SUB(curdate(), INTERVAL 1 DAY);

вижте SQL Fiddle с демонстрация