I have such a query:
SELECT
*,
(
SELECT COUNT(DISTINCT client_id)
FROM 1097_course_students_tbl
WHERE course_cycl_id=id
AND stts_id <> 8
AND client_id IN(SELECT id FROM 1097_clients_tbl WHERE is_removed=0)
) AS cnt
FROM 1097_course_cycle_tbl
WHERE (course_id IN (SELECT id FROM 1097_courses_tbl WHERE is_removed=2))
ORDER BY start_date DESC
I need to make it more efficient because it takes too long
any suggestions ?
thanks
Try the following
SELECT cc.*,IFNULL(q.cnt,0) cnt
FROM 1097_course_cycle_tbl cс
JOIN 1097_courses_tbl с ON c.id=cc.course_id AND c.is_removed=2
LEFT JOIN
(
SELECT cs.course_cycl_id,COUNT(DISTINCT cs.client_id) cnt
FROM 1097_course_students_tbl cs
JOIN 1097_clients_tbl c ON cs.client_id=c.id AND c.is_removed=0
WHERE cs.stts_id<>8
GROUP BY cs.course_cycl_id
) q
ON q.course_cycl_id=cс.id
ORDER BY cc.start_date DESC
I think id in 1097_courses_tbl and 1097_clients_tbl is primary key.
Therefore I replaced IN into JOIN.
And I converted the subquery from SELECT block wich executed for each rows into the subquery with GROUP BY which using in LEFT JOIN. Here it'll execute only one time and return all the necessary information.
Related
Server won't byte on this query, it takes too long to execute:
select prodavac.id, count(artikl.id) as brojartikala, count(poruceno.id) as brojporudzbina from prod_prodavac prodavac
inner join prod_artikl artikl
on prodavac.id=artikl.prodavacid
inner join prod_poruceno poruceno
on prodavac.id=poruceno.prodavacid
group by prodavac.id
On the other hand, both semi-queries run mega fast:
select prodavac.id, count(artikl.id) as brojartikala from prod_prodavac prodavac
inner join prod_artikl artikl
on prodavac.id=artikl.prodavacid
group by prodavac.id
Also the other one:
select prodavac.id, count(poruceno.id) as brojporudzbina from prod_prodavac prodavac
inner join prod_poruceno poruceno
on prodavac.id=poruceno.prodavacid
group by prodavac.id
order by prodavac.id asc
I would really like to do it in one query, so how to merge them correct way? All IDs are indexed integers.
Explain select shows this:
Depending on the relations between the tables and the data, your combined query might not even return the desired result. For a simple count of relations you can use correlated subqueries in the SELECT clause:
select prodavac.id, (
select count(*)
from prod_artikl artikl
where artikl.prodavacid = prodavac.id
) as brojartikala, (
select count(*)
from prod_poruceno poruceno
where poruceno.prodavacid = prodavac.id
) as brojporudzbina
from prod_prodavac prodavac
order by prodavac.id asc
This almost seems like a scope issue- the select statement in the subquery doesn't recognize table 'candidate':
SELECT
candidate.id AS id,
candidate.image AS image,
candidate.name AS name,
candidate.party AS party,
player.order AS player_order,
c_pcts.pct AS pct
FROM `candidate`
INNER JOIN players player ON player.candidate_id = candidate.id
INNER JOIN lineups lineup ON player.lineup_id = lineup.id
INNER JOIN (
SELECT
pct
FROM candidate_pcts p
INNER JOIN weekly_game game ON p.weekly_game_id = (
SELECT id FROM weekly_game ORDER BY date DESC LIMIT 1
) WHERE p.candidate_id = candidate.id
) c_pcts
WHERE lineup.id = '31'
ORDER BY player.order ASC
gives the error: "Unknown column 'candidate.id' in 'where clause'." If instead of "FROM candidate_pcts p" I put
FROM candidate_pcts p, candidate c
then it doesn't see 'p.weekly_game_id' ...huh?
Seems like I need to identify the 'candidate' table for the subquery somehow but everything I'm trying leads me only further astray. And I have tried a mess of things: order of the tables, explicitly identifying them everywhere i could think of, backticks. I should note that the nested subquery works like a charm. Here it is again:
SELECT
pct
FROM `candidate_pcts`
INNER JOIN weekly_game game ON candidate_pcts.weekly_game_id = (
SELECT id FROM weekly_game ORDER BY date DESC LIMIT 1
) WHERE candidate_pcts.candidate_id = '5'
with a hardcoded an id value there, of course. I can supply database structure if needed here, but this is long already. The 'weekly_game' table is simply a set of scores for each candidate each week and we only want the most recent week's score, thus the 'ORDER BY date DESC LIMIT 1' clause.
Thanks very much for your time.
Tables:
table candidate: {id, image, name, party}
table candidate_pcts: {id, candidate_id, pct, weekly_game_id}
table lineups: {id, date, user_id}
table players: {id,candidate_id,lineup_id,order}
table weekly_game: {id,date}
You are basically on the right track around the problem. In essence the nested sub-select does not know about candidate.id. It you break apart the query and just look at the sub-select in question:
SELECT
pct
FROM candidate_pcts p
INNER JOIN weekly_game game ON p.weekly_game_id = (
SELECT id FROM weekly_game ORDER BY date DESC LIMIT 1
) WHERE p.candidate_id = candidate.id
You can see there is NO reference whatsoever in that query to the candidate table other than in your where clause, thus this is an unknown column.
Since a subselect is, in essence, made before the outer select that references it, the subselect must be a standalone, executable query.
Thanks to all, especially Mike for that excellent explanation. What I did was restructured the query like so:
SELECT
candidate.id AS id,
candidate.image AS image,
candidate.name AS name,
candidate.party AS party,
player.order AS player_order,
pcts.pct AS pct
FROM `candidate`
INNER JOIN players player ON player.candidate_id = candidate.id
INNER JOIN lineups lineup ON player.lineup_id = lineup.id
LEFT JOIN (
SELECT
p.candidate_id AS pct_id, pct AS pct
FROM candidate_pcts p
INNER JOIN weekly_game game ON p.weekly_game_id = (
SELECT id FROM weekly_game ORDER BY date DESC LIMIT 1
)
) pcts
ON pct_id = candidate.id
WHERE lineup.id = '$lineup_id'
ORDER BY player.order ASC
I have the following 2 queries.
Query 1 :
select distinct(thread_id) from records where client_name='MyClient'
Query 2 :
select max(thread_no) from records
where thread_id='loop_result_from_above_query' AND action='Reviewed'
Is it possible to combine them into a single query ?
The second query is run on every result of the first query.
Thank you.
See attached image of a small snippet of mysql records.
I need a single mysql query to output only records which have action="MyAction" as the latest records for a given set of thread_ids. In the sample data set : record with Sr: 7201
I hope this helps in helping me :)
SELECT client_name, thread_id, MAX(thread_no) max_thread
FROM records
WHERE action='Reviewed' AND client_name='MyClient'
GROUP BY client_name, thread_id
UPDATE 1
SELECT a.*
FROM records a
INNER JOIN
(
SELECT thread_id, max(sr) max_sr
FROM records
GROUP BY thread_id
) b ON a.thread_id = b.thread_id AND
a.sr = b.max_sr
WHERE a.action = 'MyAction'
You can use SELF JOIN, but it is not advisable and will impact your query performance. Please check below query for your reference
SELECT DISTINCT r1.thread_id, MAX(r2.thread_no) from records r1 LEFT JOIN records r2 ON r2.thread_id=r1.thread_id WHERE r1.client_name='MyClient' AND r2.action='Reviewed'
SELECT a.maxthreadid,
b.maxthreadno
FROM (SELECT DISTINCT( thread_id ) AS MaxThreadId
FROM records
WHERE client_name = 'MyClient') a
CROSS JOIN (SELECT Max(thread_no) AS MaxThreadNo
FROM records
WHERE thread_id = 'loop_result_from_above_query'
AND action = 'Reviewed') b
Try this.
SELECT *
FROM (SELECT Row_number()
OVER (
partition BY thread_id
ORDER BY thread_no) no,
Max(thread_no)
OVER(
partition BY thread_id ) Maxthread_no,
thread_id,
action,
client_name
FROM records
Where client_name = 'MyClient') AS T1
WHERE no = 1
AND action = 'Reviewed'
I'm have two mysql dbs:db_system and db_events, and
I need get the last event(db_events) for every device(db_system)
SELECT * FROM db_events.events WHERE db_events.events.device_id IN (
SELECT device_id
FROM db_system.devices
WHERE db_system.devices.vendor = 1)
ORDER BY db_events.events.id DESC LIMIT 1
But I can't reach to get it, I'm only getting one record, I don't figure out how to get it, please can somebody help me?
Thanks a lot.
This should work using the MAX(Id) for each Device_ID:
SELECT e.*
FROM db_events.events e
JOIN (
SELECT Max(id) MaxId, device_id
FROM db_events.events
GROUP BY device_id ) e2 on e.Id = e2.MaxId AND e.device_id = e2.device_id
WHERE e.device_id IN (
SELECT device_id
FROM db_system.devices
WHERE vendor = 1)
ORDER BY e.id DESC
You probably don't need the ORDER BY any longer -- I just left it there in case that's how you wanted your results.
Also, this does assume that the Max(Id) is what determines your latest event for each device -- I'm assuming this since you were ordering by id DESC above. If not, you can use a DateTime column instead with the same logic.
How could I count rows from a SELECT query as a value?
Such as
SELECT FUCNTIONIMLOOKINGFOR(SELECT * FROM anothertable) AS count FROM table;
So that count is an integer of how many rows the subquery SELECT * FROM anothertable returns.
EDIT
SELECT p.PostPID, p.PostUID, p.PostText, p.PostTime, u.UserUID, u.UserName, u.UserImage, u.UserRep,
(
SELECT COUNT(f.FlagTime)
FROM Flags as f
JOIN Posts as p
ON p.PostPID = f.FlagPID
) as PostFlags
FROM Posts AS p
JOIN Users AS u
ON p.PostUID = u.UserUID
ORDER BY PostTime DESC
LIMIT 0, 30
SELECT ( SELECT COUNT(id) FROM aTable ) as count FROM table
I assume your example is a truncated version of your actual query, so perhaps you should post what you are after to get a, possibly, more optimal query.
EDIT
Working directly from my brain, something like this should be more optimal.
SELECT p.PostPID, p.PostUID, p.PostText, p.PostTime, u.UserUID, u.UserName, u.UserImage, u.UserRep, COUNT(v.FlagTime) as postFlags
FROM Flags as f
JOIN Posts as p ON p.PostPID = f.FlagPID
JOIN Users AS u ON p.PostUID = u.UserUID
LIMIT 0, 30
GROUP BY p.PostPID
ORDER BY PostTime DESC
You can say
SELECT COUNT(*) FROM anothertable
which will return a numeric value, which you can use in another query, such as in the select list of another query, or as a condition in another query.
SELECT someVariable FROM table
WHERE (SELECT COUNT(*) FROM anotherTable) > 5
OR
SELECT someVariable, (SELECT COUNT(*) FROM anotherTable) as count FROM table