I have two tables (User and Salary). I want to do a left join from User to Salary. For each user I want their name and salary. In case they have no salary that field can be left empty. So far a left join is all we need. But I only want one row per user. Due to some defects there can be several salaries for one user (see table salary). I only want one row per user which can be selected randomly (or top 1). How do I do that? The expected output is presented in the bottom.
User Table:
User Name
1 Adam
2 Al
3 Fred
Salary Table
User Salary
1 1000
2 2000
2 2000
Expected table:
User Name Salary
1 Adam 1000
2 Al 2000
3 Fred null
Changed User to Userid as User is a reserved word in SQL
SELECT u.Userid, u.Name, MAX(S.Salary)
FROM Usertable u
LEFT JOIN Salarytable s ON u.Userid = s.userid
GROUP BY u.userid, u.name
SQL Fiddle: http://sqlfiddle.com/#!6/ce4a8/1/0
Try this:
select U.User, U.Name, min(S.Salary)
from UserTable U
left join SalaryTable S on S.User = U.User
group by U.User, U.Name
You can utilize a ROW_NUMBER to get the max (or min) salary:
SELECT *
FROM Usertable u
LEFT JOIN
(
select Userid, Salary,
row_number()
over (partition by Userid
order by Salary desc) as rn
from Salarytable
) as s
ON u.Userid = s.userid
AND rn = 1
And in Teradata you could apply the rn = 1filter using QUALIFY within the Derived Table:
SELECT *
FROM Usertable u
LEFT JOIN
(
select Userid, Salary,
row_number()
over (partition by Userid
order by Salary desc) as rn
from Salarytable
qualify rn = 1
) as s
ON u.Userid = s.userid
Use a derived table to get distinct rows from salaries table.
select u.userid, u.username, s.salary
from users u left join (select distinct userid, salary from salaries) s
on u.userid = s.userid
Also, renamed tables and columns. Table names should normally end with s (since pluralis.) Columns should not.
Or, do a GROUP BY:
select u.userid, u.username, max(s.salary)
from users u left join salaries s
on u.userid = s.userid
group by u.userid, u.username
Or skip the left join, instead do a correlated sub-query:
select u.userid, u.username, (select max(s.salary) from salaries s
where u.userid = s.userid)
from users
Try this
select distinct U.User, U.Name, S.Salary
from UserTable U
left join SalaryTable S on S.User = U.User
Related
I have a query that selects users with the districts which they visited and visits count.
select users.id, places.district, count(users.id) as counts from users
left join visits on users.id = visits.user_id
inner join places on visits.place_id = places.id
group by users.id, places.district
I need to select only those users who have visited provided district the most. For example, I have a user with id 1 who visited district A one time and district B three times. If I provide district B as parameter, user 1 will be in select. If I want to select users from district A, user 1 will not be in select.
I think that's ranking, then filtering:
select *
from (
select u.id, p.district, count(*) as cnt_visits,
rank() over(partition by u.id order by count(*) desc)
from users u
inner join visits v on u.id = v.user_id
inner join places p on p.id = v.place_id
group by u.id, p.district
) t
where rn = 1 and district = ?
Note that you don't actually need table users to get this result. We could simplify the query as:
select *
from (
select v.user_id, p.district, count(*) as cnt_visits,
rank() over(partition by u.id order by count(*) desc)
from visits v
inner join places p on p.id = v.place_id
group by v.user_id, p.district
) t
where rn = 1 and district = ?
This query handles top ties: if a user had the same, maximum number of visits in two different districts, both are taken into account. If you don't need that feature, then we can simplify the subquery with distinct on:
select *
from (
select distinct on (v.user_id) v.user_id, p.district, count(*) as cnt_visits
from visits v
inner join places p on p.id = v.place_id
group by v.user_id, p.district
order by v.user_id, cnt_visits desc
) t
where district = ?
I have 2 tables
Table Users:
UserID | Name
Table Cars:
CarID | Car Name | FK_UserID
A user can have more than 1 car.
I want to join each user with 1 car only, not more.
Having looked at other threads here,
I've tried the following:
Select users.UserID, users.name, carid
from Users
join cars
on users.UserID =
(
select top 1 UserID
from users
where UserID = CarID
)
But it still returns more than 1 match for each user.
What am I doing wrong?
You can try like below using ROW_NUMBER() function
select userid, username, carname
from
(
Select users.UserID as userid,
users.name as username,
cars.carname as carname,
ROW_NUMBER() OVER(PARTITION BY users.UserID ORDER BY users.UserID) AS r
from Users
join cars
on users.UserID = cars.FK_UserID
) XXX
where r = 1;
with x as
(select row_number() over(partition by userid order by carid) as rn,
* from cars)
select u.userid, x.carid, x.carname
from users u join x on x.userid = u.userid
where x.rn = 1;
This is one way to do it using row_number function.
Another way to do it
select u.UserID,
u.name,
(select TOP 1 carid
from cars c
where u.UserID = c.FK_UserID
order by carid) carid -- Could be ordered by anything
from Users u
-- where only required if you only want users with cars
where exists (select * from car c where u.UserID = c.FK_UserID)
Best would be to do a subquery and use a group-by in it to return only 1 user and a car for each user. Then join that to the outer user table.
Here is an example:
select *
from user_table u
join (
select userid
, max(carname)
from cars
group by userid
) x on x.userId = u.userId
or you could use the row_number() examples above if you want a specific order (either this example or theirs will do the trick)
I have these tables: users, comments, ratings, and items
I would like to know if it is possible to write SQL query that basically does this:
user_id is in each table. I'd like a SQL query to count each occurrence in each table (except users of course). BUT, I want some tables to carry more weight than the others. Then I want to tally up a "score".
Here is an example:
user_id 5 occurs...
2 times in items;
5 times in comments;
11 times in ratings.
I want a formula/point system that totals something like this:
items 2 x 5 = 10;
comments 5 x 1 = 5;
ratings 11 x .5 = 5.5
TOTAL 21.5
This is what I have so far.....
SELECT u.users
COUNT(*) r.user_id
COUNT(*) c.user_id
COUNT(*) i.user_id
FROM users as u
JOIN COMMENTS as c
ON u.user_id = c_user_id
JOIN RATINGS as r
ON r.user_id = u.user_id
JOIN ITEMS as i
i.user_id = u.user_id
WHERE
????
GROUP BY u.user_id
ORDER by total DESC
I am not sure how to do the mathematical formula portion (if possible). Or how to tally up a total.
Final Code based on John Woo's Answer!
$sql = mysql_query("
SELECT u.username,
(a.totalCount * 5) +
(b.totalCount) +
(c.totalCount * .2) totalScore
FROM users u
LEFT JOIN
(
SELECT user_id, COUNT(user_id) totalCount
FROM items
GROUP BY user_id
) a ON a.user_id= u.user_id
LEFT JOIN
(
SELECT user_id, COUNT(user_id) totalCount
FROM comments
GROUP BY user_id
) b ON b.user_id= u.user_id
LEFT JOIN
(
SELECT user_id, COUNT(user_id) totalCount
FROM ratings
GROUP BY user_id
) c ON c.user_id = u.user_id
ORDER BY totalScore DESC LIMIT 10;");
Maybe this can help you,
SELECT u.user_ID,
(a.totalCount * 5) +
(b.totalCount) +
(c.totalCount * .2) totalScore
FROM users u LEFT JOIN
(
SELECT user_ID, COUNT(user_ID) totalCount
FROM items
GROUP BY user_ID
) a ON a.user_ID = u.user_ID
LEFT JOIN
(
SELECT user_ID, COUNT(user_ID) totalCount
FROM comments
GROUP BY user_ID
) b ON b.user_ID = u.user_ID
LEFT JOIN
(
SELECT user_ID, COUNT(user_ID) totalCount
FROM ratings
GROUP BY user_ID
) c ON c.user_ID = u.user_ID
ORDER BY totalScore DESC
but based on yur query above,thismay also work
SELECT u.users
(COUNT(*) * .5) +
COUNT(*) +
(COUNT(*) * 2) totalcore
FROM users as u
LEFT JOIN COMMENTS as c
ON u.user_id = c_user_id
LEFT JOIN RATINGS as r
ON r.user_id = u.user_id
LEFT JOIN ITEMS as i
ON i.user_id = u.user_id
GROUP BY u.user_id
ORDER by totalcore DESC
The only difference is by using LEFT JOIN. You will not use INNER JOIN in this situation because there are chances that user_id is not guaranteed to exists on every table.
Hope this makes sense
Here's an alternative approach:
SELECT
u.user_id,
SUM(s.weight) AS totalScore
FROM users u
LEFT JOIN (
SELECT user_id, 5.0 AS weight
FROM items
UNION ALL
SELECT user_id, 1.0
FROM comments
UNION ALL
SELECT user_id, 0.5
FROM ratings
) s
ON u.user_id = s.user_id
GROUP BY
u.user_id
I.e. for every occurrence of every user in every table, a row with a specific weight is produced. The UNIONed set of weights is then joined to the users table for subsequent grouping and aggregating.
I have a temporary table I'm creating in a sproc that houses my user information. I need to join this table to another table that has SEVERAL rows for that particular user but I only want to return one result from the "many" table.
something like this
SELECT u.firstname, u.lastname
FROM #users AS u
INNER JOIN OtherTable AS ot on u.userid = (top 1 ot.userid)
obviously that wont' work but that's the gist of what I'm trying to do for two reasons, one I only want one row returned (by a date field descending) and two for optimaztion purposes. The query has to scan several thousand rows as it currently is..
SELECT
u.firstname, u.lastname, t.*
FROM
#users AS u
CROSS APPLY
(SELECT TOP 1 *
FROM OtherTable AS ot
WHERE u.userid = ot.userid
ORDER BY something) t
Use the ROW_NUMBER() function to order your rows by datetime and then filter by row_num = 1
;WITH otNewest
AS
(
SELECT *
FROM othertable
WHERE ROW_NUM() OVER(partition by userid order by datetime DESC) = 1
)
SELECT u.firstname, u.lastname, o.*
FROM #users U
INNER JOIN otNewest O
ON U.userid = O.userid
So, if you're joining but not returning any columns from OtherTable, then you're only interested in checking for existence?
SELECT u.firstname, u.lastname
FROM #users AS u
WHERE EXISTS(SELECT 1
FROM OtherTable ot
WHERE u.userid = ot.userid)
I have a submission table that is very simple: userId, submissionGuid
I want to select the username (simple inner join to get it) of all the users who have more than 10 submissions in the table.
I would do this with embedded queries and a group by to count submissions... but is there a better way of doing it (without embedded queries)?
Thanks!
This is the simplest way, I believe:
select userId
from submission
group by userId
having count(submissionGuid) > 10
select userId, count(*)
from submissions
having count(*) > 10
group by userId
SELECT
username
FROM
usertable
JOIN submissions
ON usertable.userid = submissions.userid
GROUP BY
usertable.username
HAVING
Count(*) > 1
*Assuming that your "Users" table is call usertable and that it has a column called "UserName"
I think the correct query is this (SQL Server):
SELECT s.userId, u.userName
FROM submission s INNER JOIN users u on u.userId = s.userId
GROUP BY s.userId, u.username
HAVING COUNT(submissionGuid) > 10
If you don't have the HAVING clause:
SELECT u.userId, u.userName
FROM users u INNER JOIN (
SELECT userId, COUNT(submissionGuid) AS cnt
FROM submission
GROUP BY userId ) sc ON sc.userId = u.userId
WHERE sc.cnt > 10
select userid, count(submissionGUID) as submitCount
from Submissions
group by userid, submitCount
having submitCount > 10