Can you explain to me what is wrong with the following query?

[Deleted user]

We are running JIRA 4.4.4 and MySQL. One of our customers has a direct access to the database and want's to execute the following query. It didn't terminate and while it's running the JIRA slows down. Can you explain to me why it is problematic and suggest how to fix it.

select cc.id, cc.fieldconfigscheme, cc.customfield, cfv.issue, fcs.configname, fcs.description, cf.cfname, cfo.sequence, cfo.customvalue, cfo.disabled, it.pname
from configurationcontext cc left outer join fieldconfigscheme fcs on fcs.id = cc.fieldconfigscheme
left outer join customfieldoption cfo on cfo.customfieldconfig = fcs.id
left outer join fieldconfigschemeissuetype fcsit on fcsit.fieldconfigscheme = fcs.id
left outer join issuetype it on it.id = fcsit.issuetype
left outer join customfield cf on cf.id = cfo.customfield
left outer join customfieldvalue cfv on cfv.customfield = cf.id 
where cc.project = 10216
order by 1,2,3,4;

[Reed Johnson · Accepted solution]

It might help to move some of the constraints on cc into a subquery. My hypothesis is that the subquery will return a smaller result set to join on, rather than performing a huge join, and filtering at the end. Mysql's query optimizer might take care of this for you, but worth a shot.

So it would look like:

select cc.id, cc.fieldconfigscheme, cc.customfield, cfv.issue, fcs.configname, fcs.description, cf.cfname, cfo.sequence, cfo.customvalue, cfo.disabled, it.pname
from 
  (select
     id, fieldconficscheme, customfield
   from configurationcontext
   where cc.project = 10216) cc
left outer join fieldconfigscheme fcs on fcs.id = cc.fieldconfigscheme
left outer join customfieldoption cfo on cfo.customfieldconfig = fcs.id
left outer join fieldconfigschemeissuetype fcsit on fcsit.fieldconfigscheme = fcs.id
left outer join issuetype it on it.id = fcsit.issuetype
left outer join customfield cf on cf.id = cfo.customfield
left outer join customfieldvalue cfv on cfv.customfield = cf.id
order by 1,2,3,4;

[Deleted user]

The slowing down would be because of the number of joins you have and the amount of data that you are trying join.

[Deleted user]

Yes, I understand, is there a way to rewrite the query so that it is more effective?