SELECT * FROM student_mentor sm INNER JOIN users u
ON sm.student_id = u.user_id
WHERE sm.teacher_id = $teacher_id
Teacher_id being the session id,
I want to see all the students that have the same mentor.
Right now if I run this I just see all of the students twice, maybe one of you knows why?
My db scheme
You are not specifying on which columns you want to do the join, so you're getting a cross reference where all records are joined to all records.
You should do something like (not sure about your column names):
SELECT * FROM student_mentor sm INNER JOIN users u
ON sm.student_id = u.user_id
WHERE sm.teacher_id = $teacher_id
Related
I have this table below
Table Assignments
AssignmentID: int
LinkedTo: varchar(50)
AssignedUser: int
AssignedBy: int
where AssignedBy and AssignedUser are foreign keys from the table Users. Here is what Users looks like
UserKey:int
Username:varchar(50)
How can I do an inner join where I get both AssignedBy and AssignedUser?
The following gives me one of them but how can I get both? By the way AssignedBy and AssignedUser are two different Users. I'm trying to get Users.Username
select Users.Username
from Assignments
INNER JOIN Users ON Assignments.UserKey = Users.UserKey
If you want both user names on one row, you have to join Users twice, like
SELECT UA.Username AS AssignedUserName, UB.Username AS AssignedByUserName
FROM Assignments A
INNER JOIN Users UA ON A.AssignedUser = UA.UserKey
INNER JOIN Users UB ON A.AssignedBy = UB.UserKey;
If your goal is to have all user names regardless wether it comes from AssignedUser or from AssignedBy, you have to use UNION
SELECT U.Username
FROM Assignments A
INNER JOIN Users U ON A.AssignedUser = U.UserKey
UNION SELECT U.Username
FROM Assignments A
INNER JOIN Users U ON A.AssignedBy = U.UserKey;
Note however that this will remove duplicate user names. If you want to keep duplicates, use UNION ALL.
You need two joins:
SELECT assigned.username AS assigned_username
assigned_by.username AS assigned_by_username
FROM assignments a
JOIN users assigned ON a.assigneduser = assigned.userkey
JOIN users assigned_by ON a.assignedby = assigned_by.userkey
i have a table users(user_id, username, password etc),
a table courses(course_id, coursename, etc)
and a table student_favouriteCourses(user_id, course_id) //both as primary key
and i would like if i know the id of the user, to search for all the courses that he has as favourites. can u help me with the join query please?
Maybe something like this:
SELECT
*
FROM
student_FavouriteCourse fav
JOIN student stu ON ( fav.user_id = stu.user_id)
JOIN courses crs ON ( fav.course_id = crs.course_id)
WHERE
fav.user_id = <yourvalue>
As an explanation:
1) this will return the student_FavouriteCourse (using "fav" as an alias) records you want
SELECT
*
FROM
student_FavouriteCourse fav
WHERE
fav.user_id = <yourvalue>
2) you then JOIN the student details (using "stu" as an alias)
JOIN student stu ON ( fav.user_id = stu.user_id)
3) you then JOIN the course details (using "crs" as an alias)
JOIN courses crs ON ( fav.course_id = crs.course_id)
Can I suggest that if you are new to JOINs and SQL, you run this query at each of steps above and then you will see how the join is working and how the resulting dataset is constructed.
EDIT: Read your post again and I see you don't actually need the student join, just the courses. Therefore:
SELECT
*
FROM
student_FavouriteCourse fav
JOIN courses crs ON ( fav.course_id = crs.course_id)
WHERE
fav.user_id = <yourvalue>
I think your trying a very basic MySQL query, can you please next time try to put your code in so we can help in your mistakes and you can learn from them?
Anyway the code youre trying to do should be something like this:
select u.id, u.username, c.coursename
from users u
left join student_favouriteCourses f on u.id = f.user_id
left join courses c on f.course_id = c.id
where u.username = '<YourUsername>'
This will return your user join with your favourite courses and then the course.
In case you want to make sure you show at least 1 course (confirm that course exist) inner join will help you:
select u.id, u.username, c.coursename
from users u
inner join student_favouriteCourses f on u.id = f.user_id
inner join courses c on f.course_id = c.id
where u.username = '<YourUsername>'
There are many ways to do those joins depends of your scenario and how you like to code that.
I leave you here a link that explains this much better.
I'm trying to pull a report where each column is selecting from a specific table set. However, one of the columns needs to pull from a completely different table set and still be included in the same report. Of course, this doesn't work:
select u.first_name, ticket_work.time_spent
FROM tickets LEFT OUTER JOIN ticket_work ON ticket_work.ticket_id = tickets.id JOIN users u
(select count(tickets.id) FROM tickets JOIN users u)
where tickets.assigned_to = u.id
...
So just the part (select count(tickets.id) FROM tickets JOIN users u) needs to be selecting from the different table set but still be included in the report.
I'm a little confused by your question. Are you wanting to return the user, the count of tickets for that user, and the amount of time spent overall? If so, something like this should work:
select u.id, u.first_name,
SUM(tw.time_spent) summed_time_spent,
COUNT(DISTINCT t.id) count_tickets
FROM users u
LEFT JOIN tickets t
ON u.id = t.assigned_to
LEFT JOIN ticket_work tw
ON tw.ticket_id = t.id
GROUP BY u.id, u.first_name
Your questions is unclear, but just generally, it sounds like you're trying to join to a derived table (i.e., a query). In that case, do this:
SELECT...
FROM...
table_A A LEFT JOIN
(SELECT keyfield, valuefield FROM table_b WHERE ...) B
ON A.keyfield = B.keyfield
Does that make sense? To make a derived table, you put a query inside of parenthesis, give it an alias ('B' in this case), and then join it to your other tables as though it were a regular table.
Don't know about your table structure but you may use a sub query for such requirement
select u.first_name, ticket_work.time_spent,(select count(tickets.id) FROM tickets where ticket.id=ticket_work.ticket_id) as myCount
FROM tickets LEFT OUTER JOIN ticket_work ON ticket_work.ticket_id = tickets.id JOIN users u
where tickets.assigned_to = u.id
I have a table called USERS that has a foreign key to the table GROUPS (a user can pertain to one or none GROUPS). The table USERS also contains a column ISDELETED (a char column with T or F).
I need a query to retrieve all the GROUPS and all the USERS that are not deleted, if all the users in a GROUP are deleted or no users are defined I need the query to return NULL for that GROUP.
I tried with the following query:
SELECT GROUPS.*, USERS.*
FROM GROUPS INNER JOIN
USERS ON GROUPS.ID = USERS.GROUPID
WHERE USERS.ISDELETED = 'F'
But this query does not returns the groups that are empty. SQL and me are not the best friends in world, some help will be great, thanks.
If you want all the groups, regardless of a match in the users table, you should use a left outer join:
SELECT GROUPS.*, USERS.*
FROM GROUPS
LEFT OUTER JOIN
USERS
ON GROUPS.ID = USERS.GROUPID AND USERS.ISDELETED = 'F'
You should just need to do a left outer join -
SELECT GROUPS.*, USERS.*
FROM GROUPS LEFT OUTER JOIN
USERS ON GROUPS.ID = USERS.GROUPID
WHERE USERS.ISDELETED = 'F'
Here's a reference I like to use to remind myself of the differences in sql joins.
You need to use the LEFT OUTER JOIN operator instead of the INNER JOIN.
----------
User
----------
user_ID(pk)
UserEmail
----------
Project_Account
----------
actno
actname
projno
projname
ProjEmpID
ProjEmpMGRID
Where ProjEmpID,ProjEmpMGRID is the user_id and ProjEmpMGRID can be null.
I need to look up the useremail and display the table project_account. I need to query with actNo which has duplicate values.
My query goes like this:
select projno,projname,actno,actname,
(select u.user_email as project_manager from project_account c left outer join users u
on u.user_id = c.ProjEmpID where actno='some no')as project_manager,
(select u.user_email as program_manager from project_account c left outer join users u
on u.user_id = c.ProjEmpMGRID where actno='someno') as program_manager
from project_account where actno='someno'
The error message I get in Oracle:
ora-01427 single row subquery returns
more than one row
As my subquery returns more than one email id, I get this error. As I said, act no is not unique. I could understand the error, but I couldn't figure out the solution. I am doing a left outer join in a subquery because there might be nulls in prog manager id.
Any help would be appreciated.
The error you are getting is that one of your subqueries (either for project_manager or program_manager) is giving you back more than one ID based on your conditions. This kind of makes sense, since multiple project accounts could have the same "actno" since you haven't specified that as a Primarky Key (pk)
furhter, rather than using subqueries, just join directly to the user tables to find the IDs
select projno,projname,actno,actname,
project_user.user_email as project_manager,
program_user.user_email as program_manager
from project_account
left join User as project_user
on project_account.ProjEmpID = project_user.user_id
left join User as program_user
on project_account.ProjEmpMGRID = program_user.user_id
where actno='someno'
What about something like:
select c.projno, c.projname, c.actno, c.actname, u.user_email as project_manager, us.user_email as program_manager
from project_account c
left outer join users u
on u.user_id = c.ProjEmpID
left outer join users us
on us.user_id = c.ProjEmpMGRID
WHERE actno = 'someno'
This way you aren't running subqueries and returning multiple results and trying to store them as one value.
Why don't you simply use this?
select projno, projname, actno, actname, (select user_email from users where user_id = pa.projempid), (select user_email from users where user_id = pa.projempmgrid)
from project_account pa