SELECT query executes for a very long time occasionally - mysql

Question

I have a really wierd problem in my MySQL InnoDB database. I have following query:
SELECT DISTINCT p.idProject AS idProject, p.name AS name, 0 AS isConfirm
FROM Projects p
JOIN team_project tp ON (p.idProject = tp.idProject)
JOIN projtimes pt ON (p.idProject = pt.idProject)
JOIN CalledTimesTbl ctt ON (p.idProject = ctt.idProject)
LEFT JOIN NextCalls nc ON (ctt.idCustomer = nc.idCustomer
AND ctt.idProject = nc.idProject)
WHERE tp.idTeam = 158
AND p.activated = 1
AND current_date >= p.projStart
AND current_date < p.confirmStart
AND pt.invitesCount < pt.maxPerPresentation
AND (nc.idCustomer IS NULL OR nc.nextCall < now())
ORDER BY p.name
Generally the query runs fine, but sometimes - for example when I set tp.idTeam = 147 it runs really slow (like 10 or 20 seconds). When I create alternative team and adjust proper tables values to have the same result with different idTeam value - the query executes in a fraction of second.
I profiled the query and noticed that when query executes slowly - there is one thing that consumes most of the time:
Copying to tmp table | 12.489197
I was a bit surprised that the query creates a tmp table but ok - it creates it every time the query executes - also when it executes fast.
I just add that db is designed well, there are all needed foreign keys, etc.
How to find the source of the slow executions and eliminate it?
EDIT: EXPLAIN results:
id select_type table type possible_keys key key_len ref rows Extra
1 SIMPLE tp ref unique_row,idTeam idTeam 4 const 56 Using temporary; Using filesort
1 SIMPLE p eq_ref PRIMARY,projStart,confirmStart PRIMARY 4 xxx.tp.idProject 1 Using where
1 SIMPLE pt ref uniq_projtimes uniq_projtimes 4 xxx.tp.idProject 1 Using where; Distinct
1 SIMPLE ctt ref idProject idProject 4 xxx.tp.idProject 3966 Using index; Distinct
1 SIMPLE nc eq_ref PRIMARY,idProject PRIMARY 8 xxx.ctt.idCustomer,xxx.tp.idProject 1 Using where; Distinct
EDIT2: Results of EXPLAIN EXTENDED first for fast query, second for the slow one.
id select_type table type possible_keys key key_len ref rows filtered Extra 1 SIMPLE tp ref unique_row,idTeam idTeam 4 const 1 100 Using temporary
1 SIMPLE p eq_ref PRIMARY,projStart,confirmStart PRIMARY 4 xxx.tp.idProject 1 100 Using where
1 SIMPLE pt ref uniq_projtimes uniq_projtimes 4 xxx.tp.idProject 1 100 Using where; Distinct
1 SIMPLE ctt ref idProject idProject 4 xxx.tp.idProject 46199 100 Using index; Distinct
1 SIMPLE nc eq_ref PRIMARY,idProject PRIMARY 8 xxx.ctt.idCustomer,xxx.tp.idProject 1 100 Using index; Distinct
id select_type table type possible_keys key key_len ref rows filtered Extra
1 SIMPLE p eq_ref PRIMARY,projStart,confirmStart PRIMARY 4 xxx.ctt.idProject 1 100 Using where
1 SIMPLE pt ref uniq_projtimes uniq_projtimes 4 xxx.ctt.idProject 1 100 Using where; Distinct
1 SIMPLE tp ref unique_row,idTeam unique_row 8 xxx.pt.idProject,const 1 100 Using where; Using index; Distinct
1 SIMPLE nc eq_ref PRIMARY,idProject PRIMARY 8 xxx.ctt.idCustomer,xxx.tp.idProject 1 100 Using index; Distinct

Answer 1

Try this adjusted query. (It will join less rows)
SELECT DISTINCT p.idProject AS idProject, p.name AS name, 0 AS isConfirm
FROM Projects p
JOIN projtimes pt ON
p.idProject = pt.idProject
AND p.activated = 1
AND current_date >= p.projStart
AND current_date < p.confirmStart
AND pt.invitesCount < pt.maxPerPresentation
JOIN team_project tp ON
p.idProject = tp.idProject
AND tp.idTeam = 158
JOIN CalledTimesTbl ctt ON (p.idProject = ctt.idProject)
LEFT JOIN NextCalls nc ON (ctt.idCustomer = nc.idCustomer
AND ctt.idProject = nc.idProject)
WHERE (nc.idCustomer IS NULL OR nc.nextCall < now())
ORDER BY p.name