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
Related
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.
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
I have table [Surgery_By] table[Surgery] table[Doctor] i'm using ASP.NET with SQL Server :
The table [Surgery_By] contains the following columns:
1-ID (PK)
2-Surgery ID (FK)
3-Doctor ID (FK)
How to Display doctors ordered by number of performed surgeries ?
Try it this way
SELECT d.id, d.fullname, COUNT(s.id) total_surgeries
FROM doctor d LEFT JOIN surgery_by s
ON d.id = s.doctor_id
GROUP BY d.id, d.fullname
ORDER BY total_surgeries DESC
Sample output:
| ID | FULLNAME | TOTAL_SURGERIES |
|----|------------|-----------------|
| 1 | John Doe | 3 |
| 2 | Jane Doe | 1 |
| 3 | Mark Smith | 0 |
Here is SQLFiddle demo
This is a stab in the dark.
Select Doctor.ID As DoctorID
,Count(*) As Count
From Doctor
Join Surgery_By
On Doctor.ID = Surgery_By.DoctorID
Group By Doctor.DoctorID
Order By Count(*)
I am not sure if you want the table Surgery incorporated (but if you do, the join will be pretty straight forward - just be sure to add selected columns to the Group By statement.)
From ASP.NET, you may select this data from a SQL Command.
I have this database in sqlite (table1):
+-----+-------+-------+
| _id | name | level |
+-----+-------+-------+
| 1 | Mike | 3 |
| 2 | John | 2 |
| 3 | Bob | 2 |
| 4 | David | 1 |
| 5 | Tom | 2 |
+-----+-------+-------+
I want to create a view with all elements of level 2 and then to add a new column indicating the order of the row in the new table. That is, I would want this result:
+-------+------+
| index | name |
+-------+------+
| 1 | John |
| 2 | Bob |
| 3 | Tom |
+-------+------+
I have tried:
CREATE VIEW words AS SELECT _id as index, name FROM table1;
But then I get:
+-------+------+
| index | name |
+-------+------+
| 2 | John |
| 3 | Bob |
| 5 | Tom |
+-------+------+
I suppose it should be something as:
CREATE VIEW words AS SELECT XXXX as index, name FROM table 1;
What should I use instead of XXXX?
When ordered by _id, the number of rows up to and including this one is the same as the number of rows where the _id value is less than or equal to this row's _id:
CREATE VIEW words AS
SELECT (SELECT COUNT(*)
FROM table1 b
WHERE level = 2
AND b._id <= a._id) AS "index",
name
FROM table1 a
WHERE level = 2;
(The computation itself does not actually require ORDER BY _id because the order of the rows does not matter when we're just counting them.)
Please note that words is not guaranteed to be sorted; add ORDER BY "index" if needed.
And this is, of course, not very efficient.
You have two options. First, you could simply add a new column with the following:
ALTER TABLE {tableName} ADD COLUMN COLNew {type};
Second, and more complicatedly, but would actually put the column where you want it, would be to rename the table:
ALTER TABLE {tableName} RENAME TO TempOldTable;
Then create the new table with the missing column:
CREATE TABLE {tableName} (name TEXT, COLNew {type} DEFAULT {defaultValue}, qty INTEGER, rate REAL);
And populate it with the old data:
INSERT INTO {tableName} (name, qty, rate) SELECT name, qty, rate FROM TempOldTable;
Then delete the old table:
DROP TABLE TempOldTable;
I'd much prefer the second option, as it will allow you to completely rename everything if need be.