I have two queries that I want to join together, but I don't know how to.
Select father, mother, guardian from students where user_id = '201209291';
I get a result of 3 IDs.
Now, I need to use those three IDs to get their personal information;
Select * from system_users where user_id = (The 3 IDs from the previous query);
How would i go about solving this problem? I thought of the result of the first query into 3 rows, but I don't know how to do that either.
Select * from system_users where user_id IN
(
Select father from students where user_id = '201209291'
UNION
Select mother from students where user_id = '201209291'
UNION
Select guardian from students where user_id = '201209291'
)
Well, you can join directly using a series of ORs in the join predicate, as long as the father, mother, and guardian columns are actually user_ids in system_users.
select usrs.*
from students s
join system_users usrs on
s.father=usrs.user_id OR
s.mother=usrs.user_id OR
s.guardian=usrs.user_id
where s.user_id = '201209291';
Why don't you use join?
Select father, mother, guardian from students as s
join system_users usrs
on s.user_id=usrs.user_id
where s.user_id = '201209291';
From the first query you will have not IDs but 3 columns.
Select father, mother, guardian from students where user_id = '201209291'.
Probably you mean
Select distinct some_id from students where user_id = '201209291'
I suggest simple:
Select * from system_users where user_id in (Select distinct some_id from students where user_id = '201209291');
Did I understand the question correctly?
Related
Students Table:
ID | Family_ID | Student_name | F_name
Families Table:
ID | F_name | Contact_No
i want to get all records from students where family_id is repeating.(basically i want to know students Brothers/Sisters records if there is any in student table.
i tried it this way but got wrong output;
SELECT students.*
FROM students
INNER JOIN families
ON families.id = students.family_id
ORDER BY families.id ASC
my query result in image: as you can see some ids are showing once others are more then once, but i think all should appear more then once.
If you want to see only relevant people you don't need to link it to the families table. You can group the student with family_id. Here is your query :
SELECT *
FROM Student
WHERE family_id IN (SELECT family_id
FROM students
GROUP BY family_id
HAVING COUNT(1)>1)
ORDER BY family_id
You could try using a join on subquery for the family_id that have more that one rows in students
SELECT students.*
FROM students
inner join (
select students.family_id
FROM students
group by students.family_id
having count(*)>1
) t on t. family_id = students.family_id
I have a relation between users and groups. Users can be in a group or not.
EDIT : Added some stuff to the model to make it more convenient.
Let's say I have a rule to add users in a group considering it has a specific town, and a custom metadata like age 18).
Curently, I do that to know which users I have to add in the group of the people living in Paris who are 18:
SELECT user.id AS 'id'
FROM user
LEFT JOIN
(
SELECT user_id
FROM user_has_role_group
WHERE role_group_id = 1 -- Group for Paris
)
AS T1
ON user.id = T1.user_id
WHERE
(
user.town = 'Paris' AND JSON_EXTRACT('custom_metadata', '$.age') = 18
)
AND T1.user_id IS NULL
It works & gives me the IDs of the users to insert in group.
But when I have 50 groups to proceed, like for 50 town or various ages, it forces me to do 50 requests, it's very slow and not efficient for my Database.
How could I generate a result for each group ?
Something like :
role_group_id user_to_add
1 1
1 2
2 1
2 3
The only way I know to do that for now is to do an UNION on several sub queries like the one above, but of course it's very slow.
Note that the custom_metadata field is a user defined field. I can't create specific columns or tables.
Thanks a lot for your help.
if I good understood you:
select user.id, grp.id
from user, role_group grp
where (user.id, grp.id) not in (select user_id, role_group_id from user_has_role_group) and user.town in ('Paris', 'Warsav')
that code give list of users and group which they not belong from one of towns..
To add the missing entries to user_has_role_group, you might want to have some mapping between those town names and their group_id's.
The example below is just using a subquery with unions for that.
But you could replace that with a select from a table.
Maybe even from role_group, if those names correlate with the user town names.
insert into user_has_role_group (user_id, group_id)
select u.user_id, g.group_id
from user u
join (
select 'Paris' as name, 1 as group_id union all
select 'Rome', 2
-- add more towns here
) g on (u.town = g.name)
left join user_has_role_group ug
on (ug.user_id = u.user_id and ug.role_group_id = g.group_id)
where u.town in ('Paris','Rome') -- add more towns here
and json_extract(u.custom_metadata, '$.age') = 18
and ug.id is null;
I need to write a SQL query to get the patients that have stayed in ALL the hospitals of the city where they live. In one city there may be several hospitals of course.
So for example, if the patient 'xxx' who lives in Washington has been in a hospital, I need to list him only if he's been in all the hospitals of Washington and no less.
This is the structure of the tables:
table patient
patientID
patientCity
table hospital
hospitalCode
hospitalCity
table hospital_stay
hospitalCode
patientID
cityStay
What's the most efficient way to do this for MySQL? Thank you!
Unfortunately, MySQL can't order before grouping, so I had to use subquery to order the result correctly before grouping it.
Have fun :)
SELECT * FROM (
SELECT
p.patientID,
hs.hospitalCode
FROM
patient p
INNER JOIN hospital h ON (p.patientCity = h.hospitalCity)
LEFT JOIN hospital_stay hs ON (p.patientID = hs.patientID AND h.hospitalCode = hs.hospitalCode)
ORDER BY 2
) AS tmp_table
GROUP BY 1
HAVING NOT ISNULL(hospitalCode)
This query should work :
Select p.patientID
, p.patientCity
from patient p
inner join hospital h on h.hospitalCity = p.patientCity
inner join hospital_stay hs on hs.hospitalCode = h.hospitalCode
--where hs.cityStay = 1
group by p.patientID, p.patientCity
having count(*) = (select count(*) from hospital
where hospitalCity = p.patientCity);
Remove the comment if cityStay is kind of a flag that says that the patient went to the hospital.
want mysql query for finding mutual friend between two friend but
I am maintain the friendship of user in one way relationship for ex.
first is users table
id name
1 abc
2 xyz
3 pqr
Now second table is friend
id user_id friend_id
1 1 2
2 1 3
3 2 3
Now here i can say that abc(id=1) is friend of xyz(id=2) now similar way the xyz is friend of abc but now i want to find mutual friend between abc(id=1) and xyz(id=2) that is pqr so I want mysql query for that.
REVISED
This query will consider the "one way" relationship of a row in the friend table to be a "two way" relationship. That is, it will consider a friend relationship: ('abc','xyz') to be equivalent to the inverse relationship: ('xyz','abc'). (NOTE: we don't have any guarantee that both rows won't appear in the table, so we need to be careful about that. The UNION operator conveniently eliminates duplicates for us.)
This query should satisfy the specification:
SELECT mf.id
, mf.name
FROM (
SELECT fr.user_id AS user_id
, fr.friend_id AS friend_id
FROM friend fr
JOIN users fru
ON fru.id = fr.user_id
WHERE fru.name IN ('abc','xyz')
UNION
SELECT fl.friend_id AS user_id
, fl.user_id AS friend_id
FROM friend fl
JOIN users flf
ON flf.id = fl.friend_id
WHERE flf.user IN ('abc','xyz')
) f
JOIN users mf
ON mf.id = f.friend_id
GROUP BY mf.id, mf.name
HAVING COUNT(1) = 2
ORDER BY mf.id, mf.name
SQL Fiddle here http://sqlfiddle.com/#!2/b23a5/2
A more detailed explanation of how we arrive at this is given below. The original queries below assumed that a row in the friend table represented a "one way" relationship, in that "'abc' ff 'xyz'" did not imply "'xyz' ff 'abc'". But additional comments from the OP hinted that this was not the case.
If there is a unique constraint on friend(user_id,friend_id), then one way to get the result would be to get all of the friends of each user, and get a count of rows for that friend. If the count is 2, then we know a particular friend_id appears for both user 'abc' and for 'xyz'
SELECT mf.id
, mf.name
FROM friend f
JOIN users uu
ON uu.id = f.user_id
JOIN users mf
ON mf.id = f.friend_id
WHERE uu.name IN ('abc','xyz')
GROUP BY mf.id, mf.name
HAVING COUNT(1) = 2
ORDER BY mf.id, mf.name
(This approach can also be extended to find a mutual friend of three or more users, by including more users in the IN list, and changing the value we compare the COUNT(1) to.
This isn't the only query that will return the specified resultset; there are other ways to get it as well.
Another way to get an equivalent result:
SELECT u.id
, u.name
FROM ( SELECT f1.friend_id
FROM friend f1
JOIN users u1
ON u1.id = f1.user_id
WHERE u1.name = 'abc'
) t1
JOIN ( SELECT f2.friend_id
FROM friend f2
JOIN users u2
ON u2.id = f2.user_id
WHERE u2.name = 'xyz'
) t2
ON t2.friend_id = t1.friend_id
JOIN users u
ON u.id = t1.friend_id
ORDER BY u.id, u.name
NOTES
These queries do not check whether user 'abc' is a friend of 'xyz' (the two user names specified in the WHERE clause). It is only finding the common friend of both 'abc' and 'xyz'.
FOLLOWUP
The queries above satisfy the specified requirements, and all the examples and test cases provided in the question.
Now it sounds as if you want a row in that relationship table to be considered a "two way" relationship rather than just a "one way" relationship. It sounds like you want to want to consider the friend relationship ('abc','xyz') equivalent to ('xyz','abc').
To get that, then all that needs to be done is to have the query create the inverse rows,, and that makes it easier to query. We just need to be careful that if both those rows ('abc','xyz') and ('xyz','abc') already exist, that we don't create duplicates of them when we invert them.
To create the inverse rows, we can use a query like this. (It's simpler to look at this when we don't have the JOIN to the users table, and we use just the id value:
SELECT fr.user_id
, fr.friend_id
FROM friend fr
WHERE fr.user_id IN (1,2)
UNION
SELECT fl.friend_id AS user_id
, fl.user_id AS friend_id
FROM friend fl
WHERE fl.friend_id IN (1,2)
It's simpler if we don't include the predicates on the user_id and friend_id table, but that could be a very large (and expensive) rowset to materialize.
try this:
given that you want to get the mutual friends of friends 1 & 2
select friend_id into #tbl1 from users where user_id = 1
select friend_id into #tbl2 from users where friend_id = 2
select id, name from users where id in(select friend_id from #tbl1 f1, #tbl2 f2 where f1.friend_id=f2.friend_id)
I have two tables namely Students & Hobbies with following structure and records:
ID,Name
-----------
9,Peter
10,Steve
ID,Hobby
-----------------
9,dancing
9,singing
10,learning
I want to JOIN these tables and get a unique record from table Students.
I am doing this right now which evolves duplicate records:
SELECT a.Name
FROM Students a
LEFT JOIN Hobbies h ON a.ID =h.ID
This gives :
Name
----------
Peter
Peter
Steve
I got the reason, this is because, the table Hobbies has two records of ID=9 , that is why duplicate records are evolved, but how to retrieve a single record? Please help.
I want this:
Name
-----------
Peter
Steve
SELECT a.ID, a.Name
FROM Students a
LEFT JOIN Hobbies h
ON a.ID = h.ID
GROUP BY a.ID, a.Name
With the GROUP BY, you could then answer questions like "How many hobbies does each student have?"
SELECT a.ID, a.Name, COUNT(*) AS Number_of_Hobbies
FROM Students a
LEFT JOIN Hobbies h
ON a.ID = h.ID
GROUP BY a.ID, a.Name
This is really not the way a JOIN should be used.
left joining an unreferenced table on a constant gets you nothing.
the answer to the question you asked is "use a DISTINCT clause":
SELECT DISTINCT a.Name FROM Students a LEFT JOIN Hobbies h ON a.ID = 9
...but really, I'm pretty sure this is not what you want to do.
based off the comments, I believe what the OP's intent was something like this:
SELECT
a.Name
FROM
Students a
WHERE
a.ID = <Student ID>;
... AND , for the hobbies reference:
SELECT DISTINCT
a.ID,
a.Name
FROM
Students a
INNER JOIN
Hobbies h ON h.ID = a.ID
WHERE
h.Hobby = <Hobby Name>;
Use the distinct keyword:
SELECT distinct a.Name
FROM Students
etc....
It eliminates duplicate rows, so you'll only get one of each name.
You are getting duplicates because Peter has 2 hobbies. If you want a single record per User do this:
select * from Student where Id in (
Select DISTINCT Id from HobbY)