I am writing a mysql query and I have a question. Can I / How do I do something like this:
select rating, user_id, (
-- in here I want to write a subquery to get the number of times the user_id in the outter query has rated this teacher
) as user_rated_frequency from teachers_rating where teacher_id = id
Essentially I am trying to get data and the frequency in which that user rated that teacher. Is it possible to use an alias from one of the items I want to select in a subquery that is still in the select and not in the where clause?
Check out this ...
SELECT rating,
user_id,
(SELECT COUNT(*)
FROM teachers_rating t1
WHERE teacher_id = 3
AND t1.user_id = t2.user_id) AS user_rated_frequency
FROM teachers_rating t2
WHERE teacher_id = 3;
or that one:
SELECT AVG (rating) AS average_rating,
user_id,
(SELECT Count(*)
FROM teachers_rating t1
WHERE teacher_id = 3
AND t1.user_id = t2.user_id) AS user_rated_frequency
FROM teachers_rating t2
WHERE teacher_id = 3
GROUP BY user_rated_frequency;
Links above show a SQL Fiddle example assuming that id is 3.
Alternatively you could have a sub query in the FROM clause:
SELECT AVG (t1.rating),
t1.user_id,
t2.user_rated_frequency
FROM teachers_rating t1,
(SELECT tr.teacher_id,
tr.user_id,
COUNT(*) AS user_rated_frequency
FROM teachers_rating tr
GROUP BY tr.teacher_id) t2
WHERE t1.teacher_id = t2.teacher_id
AND t1.user_id = t2.user_id
GROUP BY user_id, user_rated_frequency
Hat a look at this Fiddle.
You need to move your subquery (technically called a derived table) into your from clause.
Something like so:
select
rating,
user_id,
from teachers_rating,
(in here I want to write a subquery to get the number of times the user_id in the outter query has rated this teacher) as user_rated_frequency f
where teacher_id = f.id
Related
I have a table having columns like: membership_id | user_id | group_id
I'm looking for a SQL query to get the number of common groups between 2 different users. I could do that in several queries and using some PHP but I'd like to know if there is a way to use only SQL for that.
Like with the user ids 1 and 3, there are 3 common groups (1, 5 and 6) so the result returned would be 3.
I've made several tests but so far no result...Thank you.
You don't need "multiple WHERE clauses" or even a self JOIN:
SELECT group_id
FROM theTable AS t
WHERE t.user_id IN (1, 3)
GROUP BY group_id
HAVING COUNT(DISTINCT user_id) = 2;
more generically
SELECT group_id
FROM theTable AS t
WHERE t.user_id IN ([user id list])
GROUP BY group_id
HAVING COUNT(DISTINCT user_id) = [# of user ids in list];
Edit: Oh, you wanted the number of groups....
SELECT COUNT(1) FROM (
SELECT group_id
FROM theTable AS t
WHERE t.user_id IN (1, 3)
GROUP BY group_id
HAVING COUNT(DISTINCT user_id) = 2
);
You can achieve this with join.
Try this:
select t1.user_id, t2.user_id, group_concat(distinct t1.group_id)
from your_table t1
join your_table t2
on t1.user_id < t2.user_id
and t1.group_id = t2.group_id
group by t1.user_id, t2.user_id;
If you don't want a concatenated output:
select distinct t1.user_id, t2.user_id, t1.group_id
from your_table t1
join your_table t2
on t1.user_id < t2.user_id
and t1.group_id = t2.group_id;
Try to join two instances of the same table (for each of them you select only the records relative to one of the users) using group_id as join attribute, and count the result:
SELECT COUNT(*)
FROM table AS t1
JOIN table AS t2 ON t1.group_id=t2.group_id
WHERE t1.user_id=1 AND t2.user_id=3;
SELECT COUNT(*)
FROM TABLE_NAME USER_ONE_INFO
TABLE_NAME USER_TWO_INFO
WHERE USER_ONE_INFO.ID = USER_ONE_ID
AND USER_TWO_INFO.ID = USER_TWO_ID
AND USER_ONE_INFO.GROUP_ID = USER_TWO_INFO.GROUP_ID;
We are having a following sqlite3 table named 'atable'
id student assignment grade
-----------------------------------
1 A 123 9
2 A 456 9
3 A 234 8
4 B 534 7
5 B 654 9
6 C 322 7
id is unique and incremented for each records. We are fetching latest assignment for each user by running query
SELECT student, assignment, grade from atable where id in
(select max(id) from atable group by student) order by id desc
This is working fine. However, we also need to fetch number of assignments for each user where user received a particular grade in the same query, say 9.
Any idea suggestion how to enhance or rewrite above query to return count as well. As mentioned, we are using sqlite3.
Thanks
You can use this correlated query:
SELECT t.student, t.assignment, t.grade,
(SELECT COUNT(*) FROM atable s
WHERE s.student = t.student and s.grade >= 9) as total_above_9
from atable t
where t.id in
(select max(id) from atable group by student)
order by t.id desc
It would be better to join to a derived table that contains an aggregated version of the original table:
select t1.student, t1.assignment, t1.grade, t2.cnt
from mytable as t1
join (
select student, max(id) as id,
count(case when grade = 9 then 1 end) as cnt
from mytable
group by student
) as t2 on t1.id = t2.id
Try this;)
select t1.student, t1.assignment, t1.grade, t2.count
from atable t1
inner join (select max(id) as id, count(if(grade=9, 1, null)) as count from atable group by student) t2
on t1.id = t2.id
order by t1.id desc
I have a location table in my database which contains location data of all the users of my system.
The table design is something like
id| user_id| longitude| latitude| created_at|
Now I have a array of user ids and I want to write a sql query to select the latest location of all these users. Can you please help me with this sql query ?
In the user_id in (......) at the end of the query you sould insert your array of user ..
select * from my_table
where (user_id , created_at) in (select user_id, max(created_at)
from my_table
group by user_id)
and user_id in ('user1','user2',... ) ;
SELECT
t1.ID,
t1.user_id,
t1.longitude,
t1.latitude,
t1.created_at
FROM
YourTable t1
INNER JOIN
(SELECT MAX(id), user_id FROM YourTable GROUP BY user_id) t2 on t2.user_id = t1.user_id
INNER JOIN
yourArrayTable ON
yourArrayTable.user_id = t1.user_id
Hi i am a newbie to SQL and have one doubt on comparing different products across multiple tables.
I have 3 tables
T1:
Product_type
order_id
T2 and T3 also has the same fields.
All the tables have different product types. They may or may not have same order ids. Its like you can order product p1 from T1 and product p2 from T2 together on the same order id o1 or they can be separate orders.
I want to find the number of orders where product type(p1) from T1 and product type(p2) from T2 are ordered in the same order(having the same order id).
I am trying to run the query like this :
select COUNT(DISTINCT order_id) as CountOf from
(
select product_type from t1
UNION ALL select product_type from t2
)
AS m
where t1.product_type = p1 and t2.product_type = p2;
What i figured out is that i cannot access t1 and t2 in the outer query since they are used in the inner query. So is there a way i can make comparision between products?
Any help would be greatly appreciated.
Thank you
Try this:
select
count(distinct t1.order_id) as OrderCount
from
t1
inner join
t2 on t1.order_id = t2.order_id
where
t1.product_type = 'p1' and
t2.product_type = 'p2'
I can't understand what you want.
But inner query scope to brackets only. So you can not access outside to brackets. try to this
select COUNT(DISTINCT order_id) as CountOf from
(
select DISTINCT order_id from t1
where t1.product_type = p1
UNION ALL
select DISTINCT order_id from t2
where t2.product_type = p2
) m
I want a query to return values not present in another table. I currently run two queries and do the intersection in code. I am stuck with the syntax for multiple columns and presence of statements after where
First query:
SELECT sid, cid
FROM Table2
where used = 0
group by sid, cid
Main query:
SELECT sid, cid, count(1) as cnt
FROM Table1
WHERE ##not any pair of (sid, cid) returned from first query##
GROUP BY sid, cid
HAVING cnt < 20
LIMIT 50
What is a complete main query?
Try:
SELECT t1.sid, t1.cid, count(1) as cnt
FROM Table1 t1
LEFT JOIN Table2 t2
ON t1.sid = t2.sid AND t1.cid = t2.cid AND t2.used = 0
WHERE t2.sid IS NULL AND t2.cid IS NULL
GROUP BY sid, cid
HAVING cnt < 20
LIMIT 50