我有三个表:wi_district, wi_group和wi_training。我需要根据地区来计算小组和培训。为此，我使用了以下SQL;
- SQL1
每个地区的查询计数组。同样,
- SQL2
查询对每个地区的训练进行计数。现在我需要组合从SQL1和SQL2获得的所有结果，并以
的形式获得结果dst_name || group_count || grp_created_date || training_count || trn_created_date
问题是每当我使用SQL1 LEFT JOIN SQL2时，它就会显示SQL1的结果，而SQL2的结果无法获得，反之亦然。请帮我解决MySQL中的这个问题
我认为您可以连接经过筛选的表，然后按地区名称分组。像这样:
SELECT dist.dst_name AS dst_name,
COUNT(grp.grp_id) AS group_count, MAX(grp.grp_created_date) AS grp_created_date,
COUNT(trn.trn_id) AS training_count, MAX(trn.trn_created_date) AS trn_created_date
FROM wi_district AS dist
LEFT JOIN (
SELECT dst_id, trn_id, trn_created_date
FROM wi_training
WHERE trn_deleted=0
AND trn_beneficiary_type IN (-1,2,8,9,10)
) AS trn ON trn.dst_id=dist.dst_id
LEFT JOIN (
SELECT grp_dst_id, grp_id, grp_created_date
FROM wi_group
WHERE grp_deleted=0
AND grp_type IN (3)
) AS grp ON grp.grp_dst_id = dist.dst_id
GROUP BY dist.dst_name
为什么使用dst_name这样的名称?最好把全名写出来，这样几个月后你也能明白它的意思。
无论如何，这个查询应该能达到目的
select d.dst_name as district
, count(distinct g.grp_id) as group_count
, max(grp_created_date) as group_created_date
, count(distinct trn_id) as training_count
, max(trn_created_date) as trn_created_date
from wi_district d
left join wi_group g on d.dst_id = g.grp_dst_id
and g.grp_deleted = 0
and g.grp_type in (3)
left join wi_training t on d.dst_id = t.dst_id
and t.trn_deleted = 0
and t.trn_beneficiary_type IN (-1,2,8,9,10)
group by d.dst_name
您需要从分组表中DRIVE它。一样。
SELECT D.dst_name, COUNT(grp_id) AS group_count, MAX(grp_created_date) as grp_created_date, COUNT(trn_id) AS training_count, MAX(trn_created_date) as trn_created_date
FROM wi_district D
LEFT JOIN wi_group G ON D.dst_id = G.grp_dst_id AND G.grp_deleted=0 AND G.grp_type IN (3)
LEFT JOIN wi_training T ON D.dst_id = T.dst_id AND T.trn_deleted=0 AND T.trn_beneficiary_type IN (-1,2,8,9,10)
GROUP BY wi_district.dst_name
如果您只需要在两个表上都存在的行，请添加子句:
WHERE NOT G.grp_dst_id IS NULL OR NOT D.dst_id IS NULL