Is there a best way to write this query? It is working just fine on workbench but when I run it on JS, it's not returning the right value.
What I want to do is I want to show users the list of all the items based on their filtered settings (basing on selected category's material and design).
Query:
SELECT COUNT(A.id)
FROM tbl_product A
JOIN tbl_product_details B ON A.id = B.prod_id
JOIN tbl_category C ON A.id = C.prod_id
JOIN tbl_material D ON A.id = D.prod_id
JOIN tbl_design E ON A.id = E.prod_id
WHERE C.category_id IN (6) AND (D.material_id IN (15) OR E.design_id IN (39));
I expect the output to be (workbench result):
COUNT(A.id): 42
instead, it's giving me:
COUNT(A.id): 1582
I am guessing that you want:
SELECT COUNT(DISTINCT A.id)
There are probably other ways to phrase the query (notably, using EXISTS), but this is the simplest modification.
Related
Can you tell me what I need to manipulate in this query to get it working?
select C.ID from
(select A.ID from CUSTOMERS A inner join PROFILES B on A.ID=B.ID where CTR='67564' and CST_CD in
('G','H')) as C
inner join
(select ID from RELATION_CODES where R_CD='KC') as R
on C.ID=R.ID
The individual inner queries are working just fine and giving correct results, not sure what is the problem with inner join in from clause..
Not completely sure I'm understanding your question, but this should be able to be rewritten without the subqueries:
select c.id
from customers c
join profiles p on c.id = p.id
join relation_codes rc on rc.id = c.id
where ctr = '67564'
and cst_cd in ('G','H')
and rc.r_cd = 'KC'
If this isn't working, please provide your table structure and sample data and expected results. This should get you pretty close though.
I have to ask, is the id field in the relation_codes table and the profiles table the same as the id in the customers table. Perhaps you need to identify how your tables are related.
A Visual Explanation of SQL Joins
A) users
B) subscribtion
C) package information
I've table where B is a link between A and C , the query selected from A where B has row id for A and join C by B id .
Full example :
SELECT a.*,c.packageTitle
FROM users AS a
LEFT JOIN subscribe AS b ON (b.userid = a.userid)
LEFT JOIN package AS c ON (b.packageid = c.packageid)
my problem if user has multi subscription in C, i cannot get latest subscription row in loop query, i also used MAX(c.packageid) inside SELECT failed also .
Goal : get latest record in B assigned by A id .
any advice is very much appreciated
I don't think you were far off by trying to use MAX() to obtain the record with the latest package ID (which assumes that this ID is an increasing auto-increment column). In my answer below, the subquery identifies the latest package ID for each user record, using a GROUP BY. This subquery is then used to filter the correct records from your original query.
SELECT a.userid, b.*
FROM users AS a
LEFT JOIN subscribe AS b
ON b.userid = a.userid
LEFT JOIN package AS c
ON b.packageid = c.packageid
INNER JOIN
(
SELECT a.userid, MAX(c.packageTitle) AS maxPackageTitle
FROM users AS a
LEFT JOIN subscribe AS b
ON b.userid = a.userid
LEFT JOIN package AS c
ON b.packageid = c.packageid
GROUP BY a.userid
) t
ON a.userid = t.userid AND c.packageTitle = t.maxPackageTitle
As a note, this query would greatly benefit from something called a Common Table Expression (CTE), which is available in other RBDMS such as SQL Server and Oracle. A CTE would make the query much less repetitive and more readable.
This should be simple enough. In Mysql you just as you said put a max on the select along with a group by. So it would look something like:
SELECT username, id_info, ...
FROM
(
SELECT a.username, a.id_info, c.packageTitle, MAX(package_id)
FROM users AS a
LEFT JOIN subscribe AS b
ON b.userid = a.userid
LEFT JOIN package AS c
ON b.packageid = c.packageid
GROUP BY a.username, a.id_info, c.packageTitle
)
Remember to list all columns in the select which are also being grouped, except the one on which you are taking the max, or the query will fail.
I have 3 tables each have almost 70,000 data
when i execute select query in which i add one inner join than it works faster.
Following works faster
select A.id from product as A
inner join product_cat as B on A.id=B.mapped_id
OR
select A.id from product as A
inner join product_sup as C on A.id = C.mapped_id
(It works faster for one inner join)
but when i add both inner join in same select query than it works too slower(Does not display data it just show loading label in phpmyadmin)
select A.id
from product as A
inner join product_cat as B
on A.id = B.mapped_id
inner join product_sup as C
on A.id = C.mapped_id
my purpose it only to find out how much record is there in database.
also tried with count function though takes too much time.
Any help will be appreciated,
Thanks,
Use EXPLAIN to analyze performance of the query and identify any missing indexes.
http://dev.mysql.com/doc/refman/5.5/en/using-explain.html
http://dev.mysql.com/doc/refman/5.5/en/explain-output.html
Add your actual query, execution plan printed by EXPLAIN and CREATE TABLE statements of all involved tables to your question if you want to get a specific advice.
Maybe your query is trying to return more than 1 million of result and that is the reason fo the slowness. Maybe you are doing a Cartesian product between tables B and C.
Let's put an example.
Table (A) = (id=1)
Table (B) = (id=1,mapped_id=1),(id=2,mapped_id=1),
(id=3,mapped_id=1),(id=4,mapped_id=1)
Table (C) = (id=1,mapped_id=1),(id=2,mapped_id=1), (id=3,mapped_id=1)
If we do that query with those data it would return 12 rows, all of them with A.id=1
To solve the problem you could try to use a DISTINCT on the SELECT clause or to do a group with the GROUP BYclase, but I think the better solution is to redesing the query depending on your goals.
If you want to use the group by your query will be something like this
select A.id from product as A
inner join product_cat as B on A.id = B.mapped_id
inner join product_sup as C on A.id = C.mapped_id
group by A.id
I tried to combine two tables' data.
I got an error like this. can you see why?
Every derived table must have its own alias
SELECT a.title, number
FROM store a
JOIN
( SELECT count(b.code) as number
FROM redeem_codes b
WHERE product = a.title
AND available = "Available")
It's a little hard tell without knowing more about your table structures. I'll give a try anyway:
SELECT a.title, count(b.code) AS number FROM store a
LEFT JOIN redeem_codes b ON b.product = a.title
WHERE b.available = "Available"
GROUP BY a.title;
you need to have ALIAS on your subquery.
SELECT a.title, number
FROM store a
JOIN (subquery) b -- b is the `ALIAS`
-- and this query will not give you the result you want
but here's a more efficient query without using subquery,
SELECT a.title, count(b.code) number
FROM store a
INNER JOIN redeem_codes b -- or use LEFT JOIN to show 0
-- for those who have no product
ON b.product = a.title
WHERE b.available = 'Available'
GROUP BY a.title
Need to generate courses list and count
all
unanswered
answered but unchecked
Questions.
My database structure is looking like that
https://docs.google.com/open?id=0B9ExyO6ktYcOenZ1WlBwdlY2R3c
Explanation for some of tables:
answer_chk_results - checked answers table. So if some answer doesn't exist on this table, it means it's unchecked
lesson_questions - lesson <-> question associations (by id) table
courses-lessons - courses <-> lessons associations (by id) table
Executing
SELECT
c.ID,
c. NAME,
COUNT(lq.id) AS Questions,
COUNT(
CASE
WHEN a.id IS NULL THEN
lq.id
END
) AS UnAnswered,
COUNT(
CASE
WHEN cr.id IS NULL THEN
lq.id
END
) AS UnChecked
FROM
courses c
LEFT JOIN `courses-lessons` cl ON cl.cid = c.id
LEFT JOIN `lesson_questions` lq ON lq.lid = cl.lid
LEFT JOIN answers a ON a.qid = lq.qid
LEFT JOIN answer_chk_results cr ON cr.aid = a.id
GROUP BY
c.ID
Tested it first on SQL fiddle with sample data. (Real data is huge, so I can't place it on sqlfiddle) It returned some values. Thought works well. But while I test it with real data, see that returns wrong values. Forex, when I manually count, result for all questions count must be 25, but it returns 27. Maybe I'm doing something wrong.
Note MySQL server running on my local machine, so I can give you teamviewer id and password if you want to connect to my desktop remotely and test query with real data.
I suspect the problem is that different joins are resulting in a multiplication of rows. The best way to fix this is by using subqueries along each dimension. The following is a more practical way. Replace the COUNTs in the select with COUNT DISTINCT:
SELECT c.ID, c. NAME,
COUNT(distinct lq.id) AS Questions,
COUNT(distinct CASE WHEN a.id IS NULL THEN lq.id END) AS UnAnswered,
COUNT(distinct CASE WHEN cr.id IS NULL THEN lq.id END) AS UnChecked
Compared to COUNT, COUNT DISTINCT is a resource hog (it has to remove duplicates). However, it will probably work fine for your purposes.
Use this query
SELECT
c.ID,
c.NAME,
COUNT(lq.id) AS Questions,
COUNT(IFNULL(a.id),lq.id)AS UnAnswered,
COUNT(IFNULL(cr.id),lq.id)AS UnChecked,
FROM courses c
LEFT JOIN `courses-lessons` cl ON cl.cid = c.id
LEFT JOIN `lesson_questions` AS lq ON lq.lid = cl.lid
LEFT JOIN answers a ON a.qid = lq.qid
LEFT JOIN answer_chk_results cr ON cr.aid = a.id
GROUP BY c.ID