I would like to optimise the query I have below:
SELECT
a.id, a.pay_point_name, a.pay_point_location,
COUNT(b.id) AS countedCustomers,
SUM(b.approved) AS summedLoans,
SUM(c.deduction) AS summedDeductions
FROM
pay_tbl a
LEFT JOIN
customer_tbl b
ON b.employer = a.pay_point_name
LEFT JOIN
loans_tbl c
ON c.paypoint = a.pay_point_name
GROUP BY
a.pay_point_name
ORDER BY
NULL
Current Execution time: 161.2s
EXPLAIN statement gives me the table below:
I would like to know how best to optimise this query and reduce execution time.
Please check this one where I've used subquery. If this works better create view with this query.
-- MySQL
SELECT t.id, t.pay_point_name
, t.pay_point_location
, COALESCE(t.countedCustomers, 0) countedCustomers
, COALESCE(t.summedLoans, 0) summedLoans
, COALESCE(p.summedDeductions, 0) summedDeductions
FROM (SELECT a.id, a.pay_point_name
, MAX(a.pay_point_location) pay_point_location
, COUNT(b.id) AS countedCustomers
, SUM(b.approved) AS summedLoans
FROM pay_tbl a
LEFT JOIN customer_tbl b
ON b.employer = a.pay_point_name
GROUP BY a.id, a.pay_point_name) t
LEFT JOIN (SELECT paypoint
, SUM(deduction) AS summedDeductions
FROM loans_tbl
GROUP BY paypoint) p
ON t.pay_point_name = p.paypoint
ORDER BY t.id;
Suppose if you have to repeatedly execute the same query frequently. You can use MySql views.
https://www.mysqltutorial.org/mysql-views-tutorial.aspx
Related
I am working on migrating from Oracle to MySQL and currently stuck on converting query with MINUS operation. I know, I have to use left join, but somehow my query is not giving the exact rows as it is in Oracle. The query is very simple with with select on views "V_*".
On Oracle:
select s.section, c.title from course c, v_staff_active s
minus
select section,title from v_rep_attended_by_section
On Mysql, I converted it like below:
select * from
( select s.section, c.title from course c, v_staff_active s) x
left join
( select section,title from v_rep_attended_by_section) y on x.section = y.section
where y.section is null;
But not getting the exact result or number of records.
Can you please help me out as I am very much new to MySQL.
Thanks in advance.
Your query should look like:
select s.section, c.title
from course c
left join v_staff_active s on c.section = s.section
and c.title = s.title
where s.section is null and s.title is null;
How can I merge these two left joins: http://sqlfiddle.com/#!9/1d2954/69/0
SELECT d.`id`, (adcount + bdcount)
FROM `docs` d
LEFT JOIN
(
SELECT da.`doc_id`, COUNT(da.`doc_id`) AS adcount FROM `docs_scod_a` da
INNER JOIN `scod_a` a ON a.`id` = da.`scod_a_id`
WHERE a.`ver_a` IN ('AA', 'AB')
GROUP BY da.`doc_id`
) ad ON ad.`doc_id` = d.`id`
LEFT JOIN
(
SELECT db.`doc_id`, COUNT(db.`doc_id`) AS bdcount FROM `docs_scod_b` db
INNER JOIN `scod_b` b ON b.`id` = db.`scod_b_id`
WHERE b.`ver_b` IN ('BA', 'BB')
GROUP BY db.`doc_id`
) bd ON bd.`doc_id` = d.`id`
to be a Single left join just to ease its use in my code, while making it no less slower?
Let me first emphasize that your method of doing the calculation is the better method. You have two separate dimensions and aggregating them separately is often the most efficient method for doing the calculation. It is also the most scalable method.
That said, your query should be equivalent to this version:
SELECT d.id,
count(distinct a.id),
count(distinct b.id)
FROM docs d left join
docs_scod_a da
ON da.doc_id = d.id LEFT JOIN
scod_a a
ON a.id = da.scod_a_id AND a.ver_a IN ('AA', 'AB') LEFT JOIN
docs_scod_b db
ON db.doc_id = d.id LEFT JOIN
scod_b b
ON b.id = db.scod_b_id AND b.ver_b IN ('BA', 'BB')
GROUP BY d.id
ORDER BY d.id;
This query is more expensive than it looks, because the COUNT(DISTINCT) incurs additional overhead compared to COUNT().
And here is the SQL Fiddle.
And, because LEFT JOIN can return NULL values, your query is more correctly written as:
SELECT d.`id`, COALESCE(adcount, 0) + COALESCE(bdcount, 0)
If you were having problems with the results, this small change might fix those problems.
Performance may be a big problem, depending on sizes of each table. It appears to be an "inflate-deflate" situation since it first "inflates" the number of rows via JOIN, then "deflates" via GROUP BY. The formulation below avoids inflation-deflation.
But first, if I understand this subquery correctly, this
SELECT da.`doc_id`, COUNT(da.`doc_id`) AS adcount
FROM `docs_scod_a` da
INNER JOIN `scod_a` a ON a.`id` = da.`scod_a_id`
WHERE a.`ver_a` IN ('AA', 'AB')
GROUP BY da.`doc_id`
can be rewritten as
SELECT `doc_id`,
( SELECT COUNT(*)
FROM `scod_a`
WHERE `id` = da.`scod_a_id`
AND `ver_a` IN ('AA', 'AB')
) AS adcount
FROM `docs_scod_a` AS da
If that is correct, then the entire query becomes
SELECT d.id,
( SELECT COUNT(*)
FROM docs_scod_a ds
JOIN scod_a s ON s.id = ds.scod_a_id
WHERE ds.doc_id = d.id
AND s.ver_a IN ('AA', 'AB')
) +
( SELECT COUNT(*)
FROM docs_scod_b ds
JOIN scod_b s ON s.id = ds.scod_b_id
WHERE ds.doc_id = d.id
AND s.ver_b IN ('BA', 'BB')
)
FROM docs AS d
Which needs these indexes:
docs_scod_a: (doc_id, scod_a_id), (scod_a_id, doc_id)
docs_scod_b: (doc_id, scod_b_id), (scod_b_id, doc_id)
scod_a: (ver_a, id)
scod_b: (ver_b, id)
docs: -- presumably has PRIMARY KEY(id)
Note the lack of GROUP BY.
docs_scod_a smells like a many-to-many mapping table. I recommend you follow the tips here.
(No COALESCE is needed since COUNT will simply return zero.)
(I don't know whether my version is better (faster or whatever) than Gordon's, nor whether my indexes will help his formulation.)
I have written an sql statement that besides all the other columns should return the number of comments and the number of likes of a certain post. It works perfectly when I don't try to get the number of times it has been shared too. When I try to get the number of time it was shared instead it returns a wrong number of like that seems to be either the number of shares and likes or something like that. Here is the code:
SELECT
[...],
count(CS.commentId) as shares,
count(CL.commentId) as numberOfLikes
FROM
(SELECT *
FROM accountSpecifics
WHERE institutionId= '{$keyword['id']}') `AS`
INNER JOIN
account A ON A.id = `AS`.accountId
INNER JOIN
comment C ON C.accountId = A.id
LEFT JOIN
commentLikes CL ON C.commentId = CL.commentId
LEFT JOIN
commentShares CS ON C.commentId = CS.commentId
GROUP BY
C.time
ORDER BY
year, month, hour, month
Could you also tell me if you think this is an efficient SQL statement or if you would do it differently? thank you!
Do this instead:
SELECT
[...],
(select count(*) from commentLikes CL where C.commentId = CL.commentId) as shares,
(select count(*) from commentShares CS where C.commentId = CS.commentId) as numberOfLikes
FROM
(SELECT *
FROM accountSpecifics
WHERE institutionId= '{$keyword['id']}') `AS`
INNER JOIN account A ON A.id = `AS`.accountId
INNER JOIN comment C ON C.accountId = A.id
GROUP BY C.time
ORDER BY year, month, hour, month
If you use JOINs, you're getting back one result set, and COUNT(any field) simply counts the rows and will always compute the same thing, and in this case the wrong thing. Subqueries are what you need here. Good luck!
EDIT: as posted below, count(distinct something) can also work, but it's making the database do more work than necessary for the answer you want to end up with.
Quick fix:
SELECT
[...],
count(DISTINCT CS.commentId) as shares,
count(DISTINCT CL.commentId) as numberOfLikes
Better approach:
SELECT [...]
, Coalesce(shares.numberOfShares, 0) As numberOfShares
, Coalesce(likes.numberOfLikes , 0) As numberOfLikes
FROM [...]
LEFT
JOIN (
SELECT commentId
, Count(*) As numberOfShares
FROM commentShares
GROUP
BY commentId
) As shares
ON shares.commentId = c.commentId
LEFT
JOIN (
SELECT commentId
, Count(*) As numberOfLikes
FROM commentLikes
GROUP
BY commentId
) As likes
ON likes.commentId = c.commentId
Please help on this query, here is sql fiddler : http://sqlfiddle.com/#!2/8acc1/1
SELECT DISTINCT c.id, v.sel_category,c.curr_tittle , c.curr_desc, v.videos_desc
FROM wp_curriculum c, wp_career_vidoes v
WHERE c.id IN
(SELECT DISTINCT curr_id
FROM wp_curriculum_category
WHERE curr_category IN (2,3)) AS I
AND I.curr_category = v.sel_category
GROUP BY I.curr_category
do you mean this?
SELECT DISTINCT c.id,
v.sel_category,
c.curr_tittle ,
c.curr_desc,
v.videos_desc
FROM wp_curriculum c
INNER JOIN wp_curriculum_category cat
ON c.id = cat.curr_id
INNER JOIN wp_career_vidoes v
ON v.sel_category = cat.curr_category
WHERE cat.curr_category IN (2,3)
SQLFiddle Demo
To further gain more knowledge about joins, visit the link below:
Visual Representation of SQL Joins
I have the following query, but after some time when users start putting in more and more items in the "ci_falsepositives" table, it gets really slow.
The ci_falsepositives table contains a reference field from ci_address_book and another reference field from ci_matched_sanctions.
How can I create a new query but still being able to sort on each field.
For example I can still sort on "hits" or "matches"
SELECT *, matches - falsepositives AS hits
FROM (SELECT c.*, IFNULL(p.total, 0) AS matches,
(SELECT COUNT(*)
FROM ci_falsepositives n
WHERE n.addressbook_id = c.reference
AND n.sanction_key IN
(SELECT sanction_key FROM ci_matched_sanctions)
) AS falsepositives
FROM ci_address_book c
LEFT JOIN
(SELECT addressbook_id, COUNT(match_id) AS total
FROM ci_matched_sanctions
GROUP BY addressbook_id) AS p
ON c.id = p.addressbook_id
) S
ORDER BY folder asc, wholename ASC
LIMIT 0,15
The problem has to be the SELECT COUNT(*) FROM ci_falsepositives sub-query. That sub-query can be written using an inner join between ci_falsepositives and ci_matched_sanctions, but the optimizer might do that for you anyway. What I think you need to do, though, is make that sub-query into a separate query in the FROM clause of the 'next query out' (that is, SELECT c.*, ...). Probably, that query is being evaluated multiple times - and that's what's hurting you when people add records to ci_falsepositives. You should study the query plan carefully.
Maybe this query will be better:
SELECT *, matches - falsepositives AS hits
FROM (SELECT c.*, IFNULL(p.total, 0) AS matches, f.falsepositives
FROM ci_address_book AS c
JOIN (SELECT n.addressbook_id, COUNT(*) AS falsepositives
FROM ci_falsepositives AS n
JOIN ci_matched_sanctions AS m
ON n.sanction_key = m.sanction_key
GROUP BY n.addressbook_id
) AS f
ON c.reference = f.addressbook_id
LEFT JOIN
(SELECT addressbook_id, COUNT(match_id) AS total
FROM ci_matched_sanctions
GROUP BY addressbook_id) AS p
ON c.id = p.addressbook_id
) AS s
ORDER BY folder asc, wholename ASC
LIMIT 0, 15