I am now having a problem sorting the data in my PHP page where the data displayed is combined of two tables as the both tables are linked by a foreign key in one of the table.
two tables are as below
Table name: Students
stu_id
stu_name
.
.
.
stu_course_id
Table name: courses
course_id
course_name
Wen displaying the data it is displayed in following format:
Student id | Student name | student course
----1 --------------john-------------engineering
----2--------------dave---------------business
I am able to sort the data by name which is pretty easy but I am having difficulty sorting the data by course name. Is this possible as the course name is not in the same table as student?
select s.stu_id, s.stu_name, c.course_name
from students s
inner join courses c on s.stu_course_id = c.course_id
order by c.course_name asc
Of course. Simply refer to the column name without ambiguity, i.e.:
ORDER BY courses.course_name
Show me your query and I'll make that work.
Yes, use the ORDER BY clause.
SELECT * FROM courses ORDER BY course_name
Related
I have a requirement for a PHP function that takes table or tables and the required columns from those db tables and returns a html table containing the data. I know how to do this for one table but am struggling with how to make this more dynamic
My thinking for one table would be to have a function that takes the table name and then an array of columns and then just selects the data from the table and then loops through it constructing the data as html and then return that from the function.
As an example my database has two tables; users and orders
users
|----------------------------|
|user_id|first_name|last_name|
|-------|----------|---------|
orders
|----------------------|
|order_id|user_id|total|
|--------|-------|-----|
Now with the function discussed above it would be easy to generate a table for all the users or orders but what I would like to do is have a function where I could dynamically join tables and for example list all users and the number of orders they've made or list all orders from user x. I know that this would be possible with many different functions but I'm really interested in developing a way of doing this dynamically and basically building all the relationships somehow in the program and then be able to call one function and request columns x,y and z
My thinking so far would be (again for this example) somehow define that number of orders for user i = count(order_id) where user_id = i
Hope this makes sense and thank you in advance
The INFORMATION_SCHEMA.KEY_COLUMN_USAGE table can be used to find all foreign key relationships from a particular table to other tables, e.g:
SELECT `TABLE_NAME`,
`COLUMN_NAME`,
`REFERENCED_TABLE_NAME`,
`REFERENCED_COLUMN_NAME`
FROM `INFORMATION_SCHEMA`.`KEY_COLUMN_USAGE`
WHERE `TABLE_SCHEMA` = SCHEMA() -- current schema
AND `REFERENCED_TABLE_NAME` IS NOT NULL
AND `TABLE_NAME` = 'orders'; -- name of table to get relationships to other tables
This should return something like the following:
+--------------+-------------+-----------------------+------------------------+
| TABLE_NAME | COLUMN_NAME | REFERENCED_TABLE_NAME | REFERENCED_COLUMN_NAME |
+--------------+-------------+-----------------------+------------------------+
| orders | user_id | users | user_id |
+--------------+-------------+-----------------------+------------------------+
The above can be done in PHP and the results can then be iterated over to dyamically construct a query that selects from those tables, joining on the listed columns. Will leave that part as an exercise ;-)
You wouldn't need to make a function to grab data from first table then loop around them and get data from the second table.
SQL can do this for you with 1 hit on the database.
All what you need to do is join the two tables, and grab the data you want..
If I understood what you need right, you want to grab all users id from the first table, and get their order count from the second table.
A simple join or selecting from both table could do that, and I suggest something like:
Select a.user_id, b.count(order_id)
FROM table1 as a, table2 as b
WHERE a.user_id = b.user_id
Group By a.user_id
Or you could join the tables and do a similar task.
I am assuming you're gonna access database from PHP code, so try that, and give me back your feedback.
This is easy to implement but we have to fix few things.
Our requirement:
1. Identify Tables according to column name.
2. How we can Join those tables.
3. How to resolve ambiguity of columns.
Solution:
Unique column name for each field or no table has duplicate column name.
To achieve it we should have fix table prefix for each table.
for example:
your column name could be odr_orderid and usr_orderid.
Now by identifying unique prefixes, we can identify tables.
Now issue arises how to join these tables
To resolve it:
Create an another table strong JOIN keys and JOin type Left, right,inner or full.
Thats all Now you can make the query as you want.
Hey I have the following MYSQL DB structure for 3 tables with many to many relation. Many users can have many cars and cars can be for many users as showing below:
Users
ID | Name
---------
100|John
101|Smith
Cars
ID | Name
---------
50|BMW
60|Audi
Users_cars
ID | UID | CID
---------
1| 100 |50
2| 100 |60
3| 101 |60
I have a page users_cars.php this page have two drop down lists
list of all users
list of all cars
In this page you can select a user from user's list and select a car from car's list then click add to insert into users_cars table.
What am trying to do is to exclude from user's drop down list all the users that have been linked with all the available cars from cars table.
In the example above user's drop down list will just have "Smith" because "John" linked with all cars available (BMW,AUDI), if "Smith" also has the BMW he will be excluded from the list. I need a select query for this condition and i don't want to use any nest select query to count user records inside users_cars table
If I understand what you are after you need to use GROUP BY in your query. So to select all users:
SELECT ID, UID FROM Users_cars GROUP BY UID
and for all cars:
SELECT ID, CID FROM Users_cars GROUP BY CID
That will group results that are the same, so you only get one instance of each user, or one instance of each car.
I hope I understood your question right.
I think you can so this using some programming -
With PHP/mysql -
Get count of all distinct car ID's
Get count of cars for each user. (making sure this lists only unique car ID's)
Loop through all users and in each loop compare the above two and exclude the user where this condition matches.
SELECT *
FROM users
WEHRE id NOT IN (SELECT uid
FROM (SELECT uid, COUNT(cid), COUNT(*)
FORM cars
LEFT OUTER JOIN users_cars ON cars.id = users_cars.cid
GROUP BY uid
HAVING COUNT(cid) = COUNT(*)
Basically, what you want to do is that (if I understood your problem) :
SELECT UID FROM Users_cars WHERE CID NOT IN (SELECT ID FROM Cars);
But carefull, this is a greedy request (depends on the size of the tables of course) and you should better put a flag on the user table and update then when your user uses the last available car (or with a batch) so you don't run the request too often !
Hi i am not sure how to put this in a brief sentences, but i have DB table like the following
User Table
user_id
username
and so on...
Item
item_id
item_name
Item_Equipped
equipped_id head (FK to item_id)
hand (FK to item_id)
user_id (FK to user_id IN User Table)
I would like to generate a query that will display like the following format
user_id | head | head_item_name | hand | hand_item_name | ...
So far i only able to do this:
SELECT user.user_id, user.username,
equipments.head, equipments.head_acc,
equipments.hand,
equipments.acc, equipments.body
FROM gw_member_equipped AS equipments
LEFT JOIN gw_member AS user ON user.memberid = equipments.member_id
Which (i have to be brutally honest) doesn't do anything much.
I tried to perform INNER JOIN between item and item_equipped however i am unable to get individual name for each item (based on its item ID)
you need to join ITEM table two times with ITEM_EQUIPPED table.
you can use below query for your desired output column shown in question..
SELECT USER.User_Id,
Item_Equipped.Head,
Item_Heads.Item_Id Head_Item_Id, -- if you want you can remove this column
Item_Heads.Item_Name Head_Item_Name,
Item_Equipped.Hand,
Item_Hands.Item_Id Hand_Item_Id, -- and this column also as these columns are same as their previous select columns
Item_Hands.Item_Name Hand_Item_Name
FROM USER, Item Item_Heads, Item Item_Hands, Item_Equipped
WHERE USER.User_Id = Item_Equipped.User_Id
AND Item_Heads.Item_Id = Item_Equipped.Head
AND Item_Hands.Item_Id = Item_Equipped.Hand
I'm working on a PHP/mySQL table that shows data I've put into my database, and I'm trying to make it sortable. I have two tables in my database:
Table "restaurant" has columns: ID and name
Table "item" has columns: ID, name and restaurantID (restaurantID is set to use the IDs from the "restaurant" table)
What I want to do is sort the restaurants by the number of times their ID shows up in the item table. I'm sure there must be a simple way to do this, Just haven't been able to figure it out. Any help would be greatly appreciated!
Try this...
select r.name, count(i.ID)
from restaurant r
left join item i on i.restaurantID = r.ID
group by r.name
order by count(i.ID) desc
I believe you can do it by using a query like following;
SELECT restaurant.*, COUNT(items.id) AS item_id FROM restaurants, items WHERE restaurant.id = items.restaurant_id ORDER BY item_id ASC;
As you may know, sorting by multiple column is possible as well;
SELECT restaurant.*, COUNT(items.id) AS item_id FROM restaurants, items WHERE restaurant.id = items.restaurant_id ORDER BY item_id ASC, restaurant.`name` DESC;
I have two tables, one called episodes, and one called score. The episode table has the following columns:
id | number | title | description | type
The score table has the following columns:
id | userId | showId | score
The idea is that users will rate a show. Each time a user rates a show, a new row is created in the score table (or updated if it exists already). When I list the shows, I average all the scores for that show ID and display it next to the show name.
What I need to be able to do is sort the shows based on their average rating. I've looked at joining the tables, but haven't really figured it out.
Thanks
To order the results, use and ORDER BY clause. You can order by generated columns, such as the result of an aggregate function like AVG.
SELECT e.title, AVG(s.score) AS avg_score
FROM episodes AS e
LEFT JOIN scores AS s ON e.id=s.showId
GROUP BY e.id
ORDER BY avg_score DESC;
You're right. You have to JOIN these tables, then use GROUP BY on the 'episodes' table's 'id' column. Then you'll be able to use AVG() function on 'the scores' tables's 'score' column.
SELECT AVG(scores.score) FROM episodes LEFT JOIN scores ON scores.showId = episodes.id GROUP BY episodes.id
SELECT episodes.*, AVG(score.score) as AverageRating FROM episodes
INNER JOIN score ON (episodes.id = score.showId)
GROUP BY episodes.id
ORDER BY AVG(score.score) DESC