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 !
Related
I have a series of tables that I want to get rows returned from in the following format:
Student ID | Last Name | First Name | Quiz Scores
-------------------------------------------------
xxxxxxx | Snow | Jon | 0,0,0,0,0,0,0,0
There's 3 relevant tables (changing any existing DB structure is not an option):
person - table of all people in the organization
enrollment - table of student and faculty enrollment data
tilt.quiz - table of quiz scores, with each row storing an individual score
The tricky part of this is the Quiz Scores. A row for the quiz score only exists if the student has taken a the quiz. Each quiz row has a module, 1 - 8. So possible quiz data for a student could be (each of these being a separate row):
person_id | module | score
---------------------------
223355 | 1 | 100
223355 | 2 | 95
223355 | 4 | 80
223355 | 7 | 100
I need the quiz scores returned in proper order with 8 comma separated values, regardless if any or all of the quizzes are missing.
I currently have the following query:
SELECT
person.id,
first_name,
last_name,
GROUP_CONCAT(tilt.quiz.score) AS scores
FROM person
LEFT JOIN enrollment ON person.id = enrollment.person_id
LEFT JOIN tilt.quiz ON person.id = tilt.quiz.person_id
WHERE
enrollment.course_id = '$num' AND enrollment_status_id = 1
GROUP BY person.id
ORDER BY last_name
The problems with this are:
It does not order the quizzes by module
If any of the quizzes are missing it simply returns fewer values
So I need the GROUP_CONCAT scores to at least include commas for missing quiz values, and have them ordered correctly.
The one solution I considered was creating a temporary table of the quiz scores, but I'm not sure this is the most efficient method or exactly how to go about it.
EDIT: Another solution would be to execute a query to check for the existence of each quiz individually but this seems clunky (a total of 9 queries instead of 1); I was hoping there was a more elegant way.
How would this be accomplished?
There are some assumptions here about your data structure, but this should be pretty close to what you're after. Take a look at the documentation for GROUP_CONCAT and COALESCE.
SELECT `person`.`id`, `person`.`first_name`, `person`.`last_name`,
GROUP_CONCAT(
COALESCE(`tilt`.`quiz`.`score`, 'N/A')
ORDER BY `tilt`.`quiz`.`module_id`
) AS `scores`
FROM `person`
CROSS JOIN `modules`
LEFT JOIN `enrollment` USING (`person_id`)
LEFT JOIN `tilt`.`quiz` USING (`person_id`, `module_id`)
WHERE (`enrollment`.`course_id` = '$num')
AND (`enrollment`.`enrollment_status_id` = 1)
GROUP BY `person`.`id`
ORDER BY `person`.`last_name`
First thing to do is use the IFNULL() function on the score
Then, use ORDER BY inside the GROUP_CONCAT
Here is my proposed query
SELECT
person.id,
first_name,
last_name,
GROUP_CONCAT(IFNULL(tilt.quiz.score,0) ORDER BY tilt.quiz.module) AS scores
FROM person
LEFT JOIN enrollment ON person.id = enrollment.person_id
LEFT JOIN tilt.quiz ON person.id = tilt.quiz.person_id
WHERE
enrollment.course_id = '$num' AND enrollment_status_id = 1
GROUP BY person.id
ORDER BY last_name
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 am having a table named tb_search_report which contains the fields search_report_id,sales_id,cat_name,search_keyword. My purpose is to create a list in the admin side of my website to get the list of the keywords used to search in the front end as well as the count of those keywords.
For that i used the following query:-
SELECT search_keyword,
cat_name,
COUNT(search_keyword) AS cnt
FROM tb_search_report GROUP BY search_keyword
The result is as follows,
search_keyword |cat_name | cnt
------------------------------------
NULL |Handbags | 6
Shoes | | 1
Fabrics | | 3
Now i need to get/list the top search results viewed in the front end along with the above table in another column. The search listing comes from tbl_sales whose primary key is sales_id. How can i display the names of the sales sales_title in top search sales from search keyword. Need help. Thanks in advance.
You can join the tables so that you can show the sales_title
SELECT tbl_sales.sales_title,tb_search_report.search_keyword,tb_search_report.cat_name,
COUNT(tb_search_report.search_keyword) AS cnt
FROM tb_search_report
INNER JOIN tbl_sales ON tb_search_report.sales_id = tbl_sales.sales_id
GROUP BY search_keyword
Just update the above query that will suit your requirements
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
I was wondering how can I have my users pick their favorite food from a category of foods in my MySQL database.
Will I need two different tables? If so what will my second table look like?
Here is my MySQL food table structure.
id | parent_id | food | url
You'll need 3 tables in total:
Food - holds food information
Users - holds users information
Users_Food - holds user id + food id (and maybe a ranking)
You should probably read up on database normalization.
You'd need to make a second table:
user_id | food_id
Make them both primary.
Then you can use JOIN's to select the food:
SELECT f.food, f.url
FROM user_food AS u
INNER JOIN food AS f ON (f.id = u.food_id)
WHERE u.user_id = {USER_ID}
This will give you a list of all favorite foods set by the user.