我有以下查询(名称已更改),它真的很慢。我不知道它这么慢是因为它可以写得更好还是因为我缺少索引。另外,我应该如何创建索引,因为大多数连接都在虚构的表上?
select y.radish, g.enton
from great g
inner join(
select sr.radish, sr.greatReferenceID
from spaceRadish sr
inner join(
select s.id
from super s
inner join experiments e
on s.CID = e.analysis) x
on sr.springID = x.id) y
on g.id = y.greatReferenceID
解释选择的输出:
'1', 'PRIMARY', '<derived2>', 'ALL', NULL, NULL, NULL, NULL, '14085960', ''
'1', 'PRIMARY', 'g', 'eq_ref', 'PRIMARY', 'PRIMARY', '4', 'y.greatReferenceID', '1', ''
'2', 'DERIVED', '<derived3>', 'ALL', NULL, NULL, NULL, NULL, '287', ''
'2', 'DERIVED', 'sr', 'ref', 'springID', 'springID', '4', 'x.id', '831666', ''
'3', 'DERIVED', 'e', 'ALL', NULL, NULL, NULL, NULL, '3271', ''
'3', 'DERIVED', 's', 'ref', 'CID,CID_2', 'CID', '767', 'cpp.e.analysis', '16', 'Using where; Using index'
最佳答案
尽量避免子查询
select y.radish, g.enton
from great g
inner join spaceRadish sr ON sr.greatReferenceID = g.id
inner join super s s.id = sr.springID
inner join experiments e on s.CID = e.analysis
并确保你在
上有正确的索引 table great composite index on (id, enton)
table spaceRadish composite index on (greatReferenceID, springID)
table super cmposite index on (id, cid)
table experiments index on analysis
关于mysql - 慢速三重内部连接,我们在Stack Overflow上找到一个类似的问题: https://stackoverflow.com/questions/56872591/