How would I do following in MySQL:
I have 3 tables:
user: id
communication: id, creation_date
user_communication: user_id, communication_id
Now I want to select all users that have had no communication since a given date.
Following is what I have now, but I'm stuck on how to get what I described above.
SELECT DISTINCT u.id FROM user u
LEFT JOIN user_communication uc ON uc.user_id = u.id
LEFT JOIN communication c ON c.id = uc.communication_id
WHERE c.creation_date < '2013-8-1';
The where condition is undoing the left join. The initial solution would be to move it to the on clause:
SELECT DISTINCT u.id FROM user u
LEFT JOIN user_communication uc ON uc.user_id = u.id
LEFT JOIN communication c ON c.id = uc.communication_id and c.creation_date < '2013-8-1';
But this doesn't do what you want. This retrieves all records. If you had a creation date field in the select clause, it would be NULL when there is record before that date.
For no communication since that date, you can do a "double" negative" query. Look for records that are since that date, and return the mismatches:
SELECT DISTINCT u.id
FROM user u LEFT JOIN
user_communication uc
ON uc.user_id = u.id LEFT JOIN
communication c
ON c.id = uc.communication_id and c.creation_date >= '2013-08-01'
WHERE c.creation_date is NULL;
EDIT:
I see. The problem is a little more subtle than my answer above. Each user has multiple communications, so none can be later. The following query tests this by grouping by u.id and then checking that there are no non-NULL values from the above join:
SELECT u.id
FROM user u LEFT JOIN
user_communication uc
ON uc.user_id = u.id LEFT JOIN
communication c
ON c.id = uc.communication_id and c.creation_date >= '2012-08-01'
group by u.id
having min(c.creation_date is null) = 1;
SELECT DISTINCT u.id FROM user u
LEFT JOIN user_communication uc ON uc.user_id = u.id
LEFT JOIN (SELECT * FROM communication WHERE creation_date < '2013-8-1') c
ON c.id = uc.communication_id
WHERE c.id is NULL;
After some research and help I have following query, which seems to work:
SELECT DISTINCT(u.id)
FROM user u
WHERE (SELECT coalesce(max(c.creation_date), '1900-01-01 00:00:00') last_creation_date
FROM user inneru
LEFT JOIN user_communication uc ON uc.user_id = inneru.id
LEFT JOIN communication c ON c.id = uc.communication_id
WHERE inneru.id = u.id) < '2012-08-01'
SQLFiddle: http://sqlfiddle.com/#!2/5dfad/10
Related
My current query:
select users.id as user_id, opportunities.id as op_id, opportunities.title, certificates.id as cert_id from opportunities
join opportunity_certificates on opportunities.id=opportunity_certificates.opportunity_id
join certificates on opportunity_certificates.certificate_id=certificates.id
join user_certificates on certificates.id=user_certificates.certificate_id
join users on user_certificates.user_id=users.id
where opportunity_certificates.is_required = 1 and
opportunities.id = 1
This produces the table on the picture below.
cert_id column can have values from 1 to 7, depends on the opportunities.id. In the table below, I want the query to return only the rows which have the same user_id but different cert_id, 1 and 2.
If the table had 3 different cert_id, I would want it to return only the rows which have same user_id but different cert_id, 1,2 and 3.
when the cert_id has only one value, query should return all the records with that one value in cert_id. Basically, it should show all users who have all required certificates.
The query has to be in the current format. I experimented with
group by users.id
having count(*) >
but I don't know how to make that comparison dynamic, relative to the count of distinctive values in the cert_id column.
Compare counts with a having condition.
select u.id as user_id --, o.id as op_id, o.title
from opportunities o
join opportunity_certificates oc on o.id=oc.opportunity_id
join certificates c on oc.certificate_id=c.id
join user_certificates uc on c.id=uc.certificate_id
join users u on uc.user_id=u.id
where oc.is_required = 1 and o.id = 1
group by u.id --,o.id,o.title
having count(distinct c.id)=(select count(distinct id) from certificates)
Useful?
with data as (
select users.id as user_id, o.title, c.id as cert_id
from opportunities o
inner join opportunity_certificates oc on oc.opportunity_id = o.id
inner join certificates c on c.id = oc.certificate_id
inner join user_certificates uc on uc.certificate_id = c.id
inner join users u on u.id = uc.user_id
where oc.is_required = 1 and o.id = 1
)
select user_id, min(title) as title, max(cert_id) as num_certs
from data
group by user_id
having count(cert_id) = (select max(cert_id) from data);
I'm assuming that cert_id values start and 1 and run sequentially. You could also use count(distinct ...) in the having clause but it guess it's debatable which ones expresses you intent more clearly.
If your version of MySQL doesn't support CTEs then you should be able to just drop that whole subquery into the having clause as well.
select u.id as user_id, min(o.title) as title, max(c.cert_id) as num_certs
from opportunities o
inner join opportunity_certificates oc on oc.opportunity_id = o.id
inner join certificates c on c.id = oc.certificate_id
inner join user_certificates uc on uc.certificate_id = c.id
inner join users u on u.id = uc.user_id
where oc.is_required = 1 and o.id = 1
group by u.id
having count(c.cert_id) = (
select max(c.cert_id)
from opportunities o
inner join opportunity_certificates oc on oc.opportunity_id = o.id
inner join certificates c on c.id = oc.certificate_id
inner join user_certificates uc on uc.certificate_id = c.id
inner join users u on u.id = uc.user_id
where oc.is_required = 1 and o.id = 1
);
Here's another one that might work if you have window functions available. (It might work with Laravel better?):
select *
from (
select users.id as user_id, o.title,
count(distinct c.id) over (partition by u.id) as user_certs,
max(c.id) over () as total_certs
from opportunities o
inner join opportunity_certificates oc on oc.opportunity_id = o.id
inner join certificates c on c.id = oc.certificate_id
inner join user_certificates uc on uc.certificate_id = c.id
inner join users u on u.id = uc.user_id
where oc.is_required = 1 and o.id = 1
) t
where user_certs = total_certs;
I am trying to write an SQL SELECT statement with a sub query. There is no error returned but I don't get the results I am expecting. The value for r.related is always NULL.
SELECT
l.id,
u.id as user_id,
u.name,
r.related
FROM
list l
INNER JOIN user u ON u.id = l.user_id
LEFT JOIN (
SELECT COUNT(u.id) AS related, b.group_id
FROM user u
INNER JOIN booking b ON b.user_id = u.id
WHERE u.id != l.user_id
AND b. = 0) AS r ON r.group_id = l.group_id
WHERE
l.group_id = 22
GROUP BY l.id, u.id
ORDER BY l.id
I am writing the sub query correctly?
Here's the problem:
SELECT COUNT(u.id) AS related, b.group_id
FROM user u
INNER JOIN booking b ON b.user_id = u.id
WHERE u.id != b.user_id
AND b. = 0
Look, you are joining user and booking table on booking.user_id = user.id
and
then you are just discarding those matching rows between these two tables in your where condition WHERE user.id != booking.user_id;
It's more like you are looking the differences between Set A and Set B in A intersection B. So in this case you won't find any (i.e. NULL).
I am trying to get the dates for when a user has last completed the course, I have the following working SQL but its giving the wrong dates.
I have dates for all modules, but know they are wrong as there a couple of months old, and I know 1 course was completed yesterday.
SELECT
u.username,
c.shortname,
DATE_FORMAT(FROM_UNIXTIME(gi.timemodified), '%d/%m/%Y') AS 'date'
FROM moodle.user u
JOIN moodle.grade_grades g ON g.userid = u.id
JOIN moodle.grade_items gi ON g.itemid = gi.id
JOIN moodle.course c ON c.id = gi.courseid
WHERE u.email = ?
GROUP BY c.shortname
The course completions should be in mdl_course_completions
SELECT u.username,
c.shortname,
cc.timecompleted
FROM mdl_course_completions cc
JOIN mdl_course c ON c.id = cc.course
JOIN mdl_user u ON u.id = cc.userid
WHERE u.email = :email
I have total 6 tables in which different info has been saved
Now i need a result in which get count from 5 tables and select all info from main table but if record does not exist than it must be need to return 0 instead of no row found that's the problem here
I have tried below query but didn't get success
SELECT
u.*,
COUNT(DISTINCT c.id) as comments,
COUNT(DISTINCT d.id) as dislikes,
COUNT(DISTINCT l.id) as likes,
COUNT(DISTINCT s.id) as shares,
COUNT(DISTINCT t.id) as tags
FROM
job_details as u
JOIN job_comments as c ON u.id = c.job_id
JOIN job_dislike as d ON u.id = d.job_id
JOIN job_like as l ON u.id = l.job_id
JOIN job_share as s ON u.id = s.job_id
JOIN job_tags as t ON u.id = t.job_id
WHERE
u.id = c.job_id AND
u.id = d.job_id AND
u.id = l.job_id AND
u.id = s.job_id AND
u.id = t.job_id
GROUP BY
u.id
This query is executed, but didn't get exact result.
I don't quite understand why.
I was hoping somebody here could help me out?
Thanks!
You probably didn't get the exact result because some tables may be missing values.
Although you can solve this problem with a LEFT JOIN, the safer solution is to pre-aggregate the data:
SELECT u.*, c.comments, d.dislikes, l.likes, s.shares, t.tags
FROM job_details as u LEFT JOIN
(select c.job_id, count(*) as comments from job_comments group by c.job_id
) c
ON u.id = c.job_id LEFT JOIN
(select d.job_id, count(*) as dislikes from job_dislike d group by d.job_id
) d
ON u.id = d.job_id LEFT JOIN
(select l.job_id, count(*) as likes from job_like l group by l.job_id
) l
ON u.id = l.job_id LEFT JOIN
(select s.job_id, count(*) as shares from job_share s group by s.job_id
) s
ON u.id = s.job_id LEFT JOIN
(select t.job_id, count(*) as tags from job_tags t group by t.job_id
) t
ON u.id = t.job_id;
Why is this better? Consider an id that has 5 comments, likes, dislikes, shares and tags. The JOIN approach produces an intermediate result with 5*5*5*5*5 = 3,125 intermediate rows. Things can really get out of hand for popular ids.
Use LEFT JOIN instead of JOIN. and you don't need WHERE clause since you have joined those tables. And, use IFNULL function to return 0 for null values. You need to modify you query like this :
SELECT u.id,
IFNULL(COUNT(DISTINCT c.id),0) as comments,
IFNULL(COUNT(DISTINCT d.id),0) as dislikes,
IFNULL(COUNT(DISTINCT l.id),0) as likes,
IFNULL(COUNT(DISTINCT s.id),0) as shares,
IFNULL(COUNT(DISTINCT t.id),0) as tags
FROM job_details as u
LEFT JOIN job_comments as c ON u.id = c.job_id
LEFT JOIN job_dislike as d ON u.id = d.job_id
LEFT JOIN job_like as l ON u.id = l.job_id
LEFT JOIN job_share as s ON u.id = s.job_id
LEFT JOIN job_tags as t ON u.id = t.job_id
GROUP BY u.id
I have two tables, users and contestants. I'm trying to select the max contestant ID that has a profile picture(which is on the user table)
Heres my terrible SQL:
SELECT u.thumbnail, u.id FROM users AS u
INNER JOIN
(
SELECT c.id, c.user_id FROM contestants AS c
WHERE u.id = c.users_id
AND c.id = (select max(c.id))
) WHERE u.thumbnail IS NOT NULL
The error currently is: #1248 - Every derived table must have its own alias.
This confuses me since Users has an alias of u, and contestants has an alias of c..
What am I doing wrong here? I'm guessing a lot so some help would be really appreciated!
Whenever you are performing a join operation, you are actually joining two table. The subquery you wrote here, for instance, is working as a separate table. Hence, you have to use an alias to this table. That's the reason behind your error message.
Your query:
SELECT u.thumbnail, u.id FROM users AS u
INNER JOIN
(
SELECT c.id, c.user_id FROM contestants AS c
WHERE u.id = c.users_id
AND c.id = (select max(c.id))
) WHERE u.thumbnail IS NOT NULL
It should contain an alias for the subquery:
SELECT c.id, c.user_id FROM contestants AS c
WHERE u.id = c.users_id
AND c.id = (select max(c.id))
Let's say, it's T.
So, your query now becomes:
SELECT u.thumbnail, u.id FROM users AS u
INNER JOIN
(
SELECT c.id, c.user_id FROM contestants AS c
WHERE u.id = c.users_id
AND c.id = (select max(c.id))
) AS T
WHERE u.thumbnail IS NOT NULL
But what you are trying to achieve, can actually be done in a neater way:
SELECT u.thumbnail, u.id, max(c.id),
FROM users as u
LEFT JOIN contestants as c
on u.id = c.user_id
WHERE u.thumbnail IS NOT NULL
Why make all the fuss when you have a better and neater approach at your disposal?
try this:
SELECT u.thumbnail, u.id
FROM users AS u
INNER JOIN
(
SELECT c.id, c.user_id FROM contestants AS c
WHERE u.id = c.users_id
AND c.id = (select max(c.id))
)A
WHERE u.thumbnail IS NOT NULL
i think this should be simple,
SELECT u.thumbnail, u.id
FROM users u
INNER JOIN contestants c
ON u.id = c.users_id
WHERE u.thumbnail IS NOT NULL
ORDER BY c.id DESC
LIMIT 1
This is very simple.
SELECT user.thumbnail, user.id
FROM users user
INNER JOIN contestants cont ON cont.id = cont.users_id
WHERE cont.thumbnail IS NOT NULL
ORDER BY user.id DESC