I read many questions here about mutual friends and following and followers but i can't solved my problem, I have two tables like these.
User_table ( UID, Name)
Relation_table (RID, UID,UIDF)
for example in user_table have 4 users
UID | Name
------------------
1 | Kim Tessman
2 | Nella Ohler
3 | Adria Larose
4 | Huey Errico
And Relation_table have these data
RID | UID | UIDF
------------------
1 | 1 | 2
2 | 2 | 1
3 | 1 | 4
4 | 4 | 3
5 | 4 | 1
my questions are :
how to get list of Mutual friends ?
how to get list of Following ?
how to get list of Followers ?
please who can solve this problem thank you :)
I am guessing that the UID column in the Relation_Table is the user and that the UIDF is the person they are following. Here is the SQL query that finds who a person is following. The who is being followed is the same query, you just focus on the other name column or switch the column order around.
Here is a list of who follows who. It is also the list of who is being followed.
SELECT FollowingUser.UID as FollowingUserID, FollowingUser.Name, BeingFollowed.UID AS BeingFollowedID, BeingFollowed.Name AS BeingFollowedName
FROM User_table AS FollowingUser INNER JOIN
Relation_Table AS r ON FollowingUser.UID = r.uid INNER JOIN
User_table AS BeingFollowed ON r.uidf = BeingFollowed.UID
And this query gives you the list of mutual friends - but it gives the inverse of the relationship. If this matters, add this to the end where FollowingUser.UID > BeingFollowed.UID
SELECT FollowingUser.UID AS FollowingUserID, FollowingUser.Name, BeingFollowed.UID AS BeingFollowedID, BeingFollowed.Name AS BeingFollowedName
FROM User_table AS FollowingUser INNER JOIN
Relation_Table AS r ON FollowingUser.UID = r.uid INNER JOIN
Relation_Table AS r1 ON r.uid = r1.uidf AND r.uidf = r1.uid INNER JOIN
User_table AS BeingFollowed ON r1.uid = BeingFollowed.UID
Related
How can I create a column that has ranked the information of the table based on two or three keys?
For example, in this table the rank variable is based on Department and Name:
Dep | Name | Rank
----+------+------
1 | Jeff | 1
1 | Jeff | 2
1 | Paul | 1
2 | Nick | 1
2 | Nick | 2
I have found this solution but it's in SQL and I don't think it applies to my case as all information is in one table and the responses seem to SELECT and JOIN combine information from different tables.
Thank you in advance
You can count how many rows come before the current row in the current group:
UPDATE MyTable
SET Rank = (SELECT COUNT(*)
FROM MyTable AS T2
WHERE T2.Dep = MyTable.Dep
AND T2.Name = MyTable.Name
AND T2.rowid <= MyTable.rowid);
(The rowid column is used to differentiate between otherwise identical rows. Use the primary key, if you have one.)
I have a query result set like this:
value | id
500 | 1
400 | 1
300 | 2
and a product table:
product_name | id
product_1 | 1
product_2 | 2
product_5 | 3
product_6 | 4
product_9 | 5
product_0 | 6
Now I want to find the product_name from product table for every row in query result set and join the result to look like following:
The result after joining should be following:
product_name | id | value
product_1 | 1 | 500
product_1 | 1 | 400
product_2 | 2 | 300
I am getting confused how to use left join to achieve the result.
You'd join based on the value that's common between the two tables; in this case, it's id.
It doesn't seem like you want any NULL values for value, so you wouldn't use a LEFT JOIN; you'd want an INNER JOIN instead.
This would get you pretty much what you want; bear in mind that this is untested.
SELECT p.product_name, qr.id, value
FROM product p
INNER JOIN query_result_set qr ON qr.id = p.id
ORDER BY value DESC;
Also, your expectations are wrong - product_5 has an id of 3, so it wouldn't appear in this join result.
I have 2 table one table is Course Category and second is Course
In Course Category Table
Following data stores :
CategoryId | Name
1 | MCA
2 | MBA
In Course Table
Following data stores :
Id | Name | CategoryId | ParentId
1 | Asp.Net | 1 | 0
2 | C# | 1 | 1
3 | Finance | 2 | 0
i want following output
Id | Name | Parent
1 | MCA | 0
2 | MBA | 0
3 | Asp.Net | 1
4 | C# | 3
5 | Finance | 2
Whether i have to use nested query or should i relate two tables with foreign and primary keys or any mapping should be done.if not give me a solution to do this.
thanks in advance
select rownum as id, name, 0 as parent
from Category
union all
select rownum, name, id
from course
I assume that you only have one level of children (no cases like parent<-child<-child)
select c.id, t.name, parent.name, c.name from course c
join category t on c.categoryId = t.id
left join (select c2.id, c2.name from course c2) parent on c.parentId = parent.id
This should give you something like
id |categoryname |parentname |coursename
1 |MCA |null |Asp.Net
2 |MCA |Asp.Net |C#
3 |MBA |null |Finance
This is not exactly your desired result but should do the trick to display what you want.
So I'm making a movie website and in my database table, I've got a column called Genre. In this I have listed the genres like this; Horror, Action.
Example Table
+----+---------+--------+
| id | Genre |
+----+---------+--------+
| 1 | Action |
| 2 | Horror, Action |
| 3 | Horror |
| 4 | Action |
| 5 | Romance, Drama |
| 6 | Horror, Drama |
+----+---------+--------+
So if I were to do a query to get films with a Horror genre, it would return the ID's 2,3 & 6. How would I go about structuring a query to do this?
Thanks.
The structure of your database is no good. Read up on database normalization to understand why this is. I would go with a structure like this:
Movie:
Id
Name
Movie_Genres
Movie_Id
Genre_Id
Genres:
Id
Name
You can then do a query like this:
SELECT m.name
FROM Movie as m
INNER JOIN Movie_Genres as mg
ON mg.Movie_id = m.id
WHERE mg.Genre_id = {Horror genre Id}
If you don't structure your DB like this you will run into a lot of problems down the road.
Continuing off of #Abe's excellent answer. If you want to build a comma delimited string based on #Abe's normalized 3 table structure it would look like this:
SELECT m.Name,
STUFF(( SELECT ', ' + g.Name
FROM Movie_Genres as mg
INNER JOIN Genres AS g on mg.Genre_id = g.Id and mg.Movie_id = m.id
FOR XML PATH('')
), 1, 2, '')
FROM Movie AS m
GROUP BY m.Name, m.Id;
Here's a Fiddle
I have A table and two rows with id=1 and id=2 and their x parameter is 1. I also have B table and two rows with same id 1 and 2. I am trying to update all of the data(column)on B table which has same id with A table whose x parameter is 1.
A table
id | x |
1 | 1 |
2 | 1 |
B table
id | Y |
1 | yes|
2 | yes|
My query is
UPDATE B SET y='No' WHERE B.id=(SELECT A.id FROM A WHERE A.x=1);
The problem is select returns mutliple data and i can only update the first data.
I tried to use JOIN but sqlite gives syntax error near INNER i couldn't find the problem.
UPDATE B SET B.y='No' INNER JOIN A ON B.id=A.id WHERE A.x=1;
Use this:
UPDATE ... WHERE B.id IN (SELECT A.id ...);