一对多 group by 后 查询 count(*) ，但是 count(*)=0的不能显示

查询在ts下面的pt已经完成的个数，但是按照下面的sql查询不出来 count(pt.id已完成)=0的ts记录
SELECT
ts.*,
COUNT(pt.id)
FROM
 trial_record ts 
LEFT JOIN trial_record tg ON ts.id = tg.p_id AND ts.trial_id = tg.trial_id
LEFT JOIN trial_record tc  ON tc.p_id = tg.id AND tc.trial_id = tg.trial_id
LEFT JOIN ptrial_record pt ON pt.trial_id = tc.trial_id AND pt.p_id = tc.id 
WHERE
  pt.finished_exams >= pt.total_exams AND
 tc.type = 4
AND tg.type = 3
AND ts.type = 2
and ts.trial_id in( 
SELECT trial_id from trial_parent_middle WHERE trial_parent_id=202)
and pt.type=2
GROUP BY ts.id 
ORDER BY t_id asc;
经考虑 ，改为：

SELECT
ts.*,
sum(case when pt.finished_exams>=pt.total_exams then 1 else 0 end) as counts
FROM
 trial_record ts 
LEFT JOIN trial_record tg ON ts.id = tg.p_id AND ts.trial_id = tg.trial_id
LEFT JOIN trial_record tc  ON tc.p_id = tg.id AND tc.trial_id = tg.trial_id
LEFT JOIN ptrial_record pt ON pt.trial_id = tc.trial_id AND pt.p_id = tc.id 
WHERE
 tc.type = 4
AND tg.type = 3
AND ts.type = 2
and ts.trial_id in( 
SELECT trial_id from trial_parent_middle WHERE trial_parent_id=202)
and pt.type=2
GROUP BY ts.id


可以查出全部结果，这个必须保证 where后边的条件都满足，若是tg和tc不存在也查不出来。