I have 2 tables, which are related on a shared column customer_id:
customer
rental
I need to display the rental_id and last_update from the rental table.
Also the active column from the customer table where active is false
I have searched multiple websites, as well as several questions here on Stack Overflow and this is the closest I have gotten:
SELECT rental_id, last_update, active
FROM rental
WHERE customer_id IN
(SELECT customer_id
FROM customer
WHERE active = false);
Thank you in advance for any help.
Edit: I have to use a subquery as this is a school project so inner join answers do not help. Sorry.
Since the subquery only returns customers where active = false, there's no need to get that column from the table, you can just hard-code it into the SELECT list.
SELECT rental_id, last_update, false AS active
FROM rental
WHERE customer_id IN (
SELECT customer_id
FROM customer
WHERE active = false)
There's no way to get non-constant data from a table without it being one of the FROM or JOIN tables.
BTW, in my experience, MySQL is often very poor at optimizing WHERE c in (SELECT ...). I try to avoid them at all costs, and I think your teacher is misguided in prohibiting them.
Try a query like this. It use INNER JOIN instead of subselect
SELECT
r.rental_id,
r.last_update,
c.active
FROM rental r
INNER JOIN
customer c ON c.cusomer_id = r.customer_id
WHERE
c.active = FALSE;
Related
My database has 3 tables. One is called Customer, one is called Orders, and one is called RMA. The RMA table has the info regarding returns. I'll include a screen shot of all 3 so you can see the appropriate attributes. This is the code of the query I'm working on:
SELECT State, SKU, count(*)
from Orders INNER JOIN Customer ON Orders.Customer_ID = Customer.CustomerID
INNER JOIN RMA ON Orders.Order_ID = RMA.Reason
Group by SKU
Order by SKU
LIMIT 10;
I'm trying to get how much of each product(SKU) is returned in each state(State). Any help would really be appreciated. I'm not sure why, but anytime I include a JOIN statement, my query takes anywhere from 5 minutes to 20 minutes to process.
[ Customer table]
!2[ RMA table]
!3
Your query should look like this:
SELECT c.State, o.SKU, COUNT(*)
FROM Orders o INNER JOIN
Customer c
ON o.Customer_ID = c.CustomerID JOIN
RMA
ON o.Order_ID = RMA.Order_Id
GROUP BY c.State, o.SKU
ORDER BY SKU;
Your issue is probably the incorrect JOIN condition between Orders and RMA.
If you have primary keys properly declared on the tables, then this query should have good-enough performance.
Given you are joining with an Orders table I'm going to assume this table contains all the orders that the company has ever done. This can be quite large and would likely cause the slowness you are seeing.
You can likely improve this query if you place some constraint on the Orders you are selecting, restricting what date range you use is common way to do this. If you provide more information about what the query is for and how large the dataset is everyone will be able to provide better guidance as to what filters would work best.
I have a table with a recursive 1:M
Every customer may have been referred by a previous customer, now I want to group the customers who have made referrals, so I can display which ones have referred the most.
and I would want a query which gave following output
I tried
SELECT count(*) AS Count_of_referrals, referral_id
FROM Customer
GROUP BY referral_id
which gives the amount of times each referral_id is mentioned, but I can't find a way to link this back to the actual customer who referred them.
Appreciate any help I can get here.. :-)
Well, you're close. You just need to self join the customer table to get the name of the referral_id in there.
SELECT c1.referral_id,
c2.name,
count(*) count_of_referrals
FROM customer c1
INNER JOIN customer c2
ON c2.customer_id = c1.referral_id
GROUP BY c1.referral_id,
c2.name;
I tried to write a query, but unfortunately I didn't succeed.
I want to know how many packages delivered over a given period by a person.
So I want to know how many packages were delivered by John (user_id = 1) between 01-02-18 and 28-02-18. John drives another car (another plate_id) every day.
(orders_drivers.user_id, plates.plate_name, orders.delivery_date, orders.package_amount)
I have 3 table:
orders with plate_id delivery_date package_amount
plates with plate_id plate_name
orders_drivers with plate_id plate_date user_id
I tried some solutions but didn't get the expected result. Thanks!
Try using JOINS as shown below:
SELECT SUM(o.package_amount)
FROM orders o INNER JOIN orders_drivers od
ON o.plate_id=od.plate_id
WHERE od.user_id=<the_user_id>;
See MySQL Join Made Easy for insight.
You can also use a subquery:
SELECT SUM(o.package_amount)
FROM orders o
WHERE EXISTS (SELECT 1
FROM orders_drivers od
WHERE user_id=<user_id> AND o.plate_id=od.plate_id);
SELECT sum(orders.package_amount) AS amount
FROM orders
LEFT JOIN plates ON orders.plate_id = orders_drivers.plate_id
LEFT JOIN orders_driver ON orders.plate_id = orders_drivers.plate_id
WHERE orders.delivery_date > date1 AND orders.delivery_date < date2 AND orders_driver.user_id = userid
GROUP BY orders_drivers.user_id
But seriously, you need to ask questions that makes more sense.
sum is a function to add all values that has been grouped by GROUP BY.
LEFT JOIN connects all tables by id = id. Any other join can do this in this case, as all ids are unique (at least I hope).
WHERE, where you give the dates and user.
And GROUP BY userid, so if there are more records of the same id, they are returned as one (and summed by their pack amount.)
With the AS, your result is returned under the name 'amount',
If you want the total of packageamount by user in a period, you can use this query:
UPDATE: add a where clause on user_id, to retrieve John related data
SELECT od.user_id
, p.plate_name
, SUM(o.package_amount) AS TotalPackageAmount
FROM orders_drivers od
JOIN plates p
ON o.plate_id = od.plate_id
JOIN orders o
ON o.plate_id = od.plate_id
WHERE o.delivery_date BETWEEN convert(datetime,01/02/2018,103) AND convert(datetime,28/02/2018,103)
AND od.user_id = 1
GROUP BY od.user_id
, p.plate_name
It groups rows on user_id and plate_name, filter a period of delivery_date(s) and then calculate the sum of packageamount for the group
I currently have 4 SQL tables that look like this:
CustomersTable, RegistrationTable, OrdersTable and OffersTable
enter image description here
I need to write a SELECT statement that retrieves all customers from the CustomersTable (all the fields) that contain rows that match the RegistrationTable Or rows that match the OrdersTable with status "closed", in the result table shouldn't display duplicate customers.
As you realized, CustomersTable and RegistrationTable have the field in common "customerId", but between CustomersTable and OrdersTable there is no field in common. However there is another table (OffersTable) which has the fields "customerId" and "ID", to query information to Customers and Orders table respectively. Remember that a customer who appears in OfferTable not necessarily will appear in OrderTable or just the status is NOT "Closed"
So based on my example tables above, if I were to run the query, it would return the following result:
enter image description here
In the result table shouldn't display duplicate customers.
I really appreciate your help.
Thanks for your time !!
Note - I am using MySQL
Try Using "Union" and "inner join" with every table Like below:
Select Customers.* from Customers inner join Registration on Customers. customerId= Registration.customerId
union
Select Customers.* from Customers inner join offers on Customers.customerId=offers.customerId
inner join Orders on orders.Id= offers.Id and Orders.Status='closed'
I would think exists or in, given what you want. Your description of the table is a bit cumbersome -- which is why sample data in the question is so helpful.
The resulting query would look something like this:
select c.*
from customers c
where exists (select 1 from registrations r where r.customerid = c.customerid) or
exists (select 1
from offers o join
orders oo
on o.id = oo.orderid
where o.customerid = c.customerid and
oo.status = 'closed'
);
The column names may not be quite right.
I'm trying to answer to the following query:
Select the first name and last name of the clients which rent films (that have DVD's) from all the categories, ordering by first name and last name.
Database consists in:
(better view - open in a new tab)
Inventory -> DVD's
Rental -> Rents customers did
Category table:
| category_id | int(10) unsigned | NO | PRI | NULL | auto_increment |
| name | varchar(25) | YES | | NULL |
My doubt is in how to assign that a field from a query must contain all ids from another query (categories).
I mean I understand the fact we can natural join inventory with rental and film, and then find an id that fails on a single category, then we know he doesn't contain all... But I can't complete this.
I have this solution (But I can't understand it very well):
SELECT first_name, last_name
FROM customer AS C WHERE NOT EXISTS
(SELECT * FROM category AS K WHERE NOT EXISTS
(SELECT * FROM (film NATURAL JOIN inventory) NATURAL JOIN rental
WHERE C.customer_id = customer_id AND K.category_id = category_id));
Are there any other solutions?
On our projects, we NEVER use NATURAL JOIN. That doesn't work for us, because the PRIMARY KEY is always a surrogate column named id, and the foreign key columns are always tablename_id.
A natural join would match id in one table to id in the other table, and that's not what we want. We also frequently have "housekeeping" columns in the tables that are named the same, such as version column used for optimistic locking pattern.
And even if our naming conventions were different, and the join columns were named the same, there would be a potential for a join in an existing query to change if we added a column to a table that was named the same as a column in another table.
And, reading SQL statement that includes a NATURAL JOIN, we can't see what columns are actually being matched, without running through the table definitions, looking for columns that are named the same. That seems to put an unnecessary burden on the reader of the statement. (A SQL statement is going to be "read" many more times than it's written... the author of the statement saving keystrokes isn't a beneficial tradeoff for ambiguity leading to extra work by future readers.
(I know others have different opinions on this topic. I'm sure that successful software can be written using the NATURAL JOIN pattern. I'm just not smart enough or good enough to work with that. I'll give significant weight to the opinions of DBAs that have years of experience with database modeling, implementing schemas, writing and tuning SQL, supporting operational systems, and dealing with evolving requirements and ongoing maintenance.)
Where was I... oh yes... back to regularly scheduled programming...
The image of the schema is way too small for me to decipher, and I can't seem to copy any text from it. Output from a SHOW CREATE TABLE is much easier to work with.
Did you have a SQL Fiddle setup?
I don't thin the query in the question will actually work. I thought there was a limitation on how far "up" a correlated subquery could reference an outer query.
To me, it looks like this predicate
WHERE C.customer_id = customer_id
^^^^^^^^^^^^^
is too deep. The subquery that's in isn't allowed to reference columns from C, that table is too high up. (Maybe I'm totally wrong about that; maybe it's Oracle or SQL Server or Teradata that has that restriction. Or maybe MySQL used to have that restriction, but a later version has lifted it.)
OTHER APPROACHES
As another approach, we could get each customer and a distinct list of every category that he's rented from.
Then, we could compare that list of "customer rented category" with a complete list of (distinct) category. One fairly easy way to do that would be to collapse each list into a "count" of distinct category, and then compare the counts. If a count for a customer is less than the total count, then we know he's not rented from every category. (There's a few caveats, We need to ensure that the customer "rented from category" list contains only categories in the total category list.)
Another approach would be to take a list of (distinct) customer, and perform a cross join (cartesian product) with every possible category. (WARNING: this could be fairly large set.)
With that set of "customer cross product category", we could then eliminate rows where the customer has rented from that category (probably using an anti-join pattern.)
That would leave us with a set of customers and the categories they haven't rented from.
OP hasn't setup a SQL Fiddle with tables and exemplar data; so, I'm not going to bother doing it either.
I would offer some example SQL statements, but the table definitions from the image are unusable; to demonstrate those statements actually working, I'd need some exemplar data in the tables.
(Again, I don't believe the statement in the question actually works. There's no demonstration that it does work.)
I'd be more inclined to test it myself, if it weren't for the NATURAL JOIN syntax. I'm not smart enough to figure that out, without usable table definitions.
If I worked on that, the first think I would do would be to re-write it to remove the NATURAL keyword, and add actual predicates in an actual ON clause, and qualify all of the column references.
And the query would end up looking something like this:
SELECT c.first_name
, c.last_name
FROM customer c
WHERE NOT EXISTS
( SELECT 1
FROM category k
WHERE NOT EXISTS
( SELECT 1
FROM film f
JOIN inventory i
ON i.film_id = f.film_id
JOIN rental r
ON r.inventory_id = i.inventory_id
WHERE f.category_id = k.category_id
AND r.customer_id = c.customer_id
)
)
(I think that reference to c.customer_id is too deep to be valid.)
EDIT
I stand corrected on my conjecture that the reference to C.customer_id was too many levels "deep". That query doesn't throw an error for me.
But it also doesn't seem to return the resultset that we're expecting, I may have screwed it up somehow. Oh well.
Here's an example of getting the "count of distinct rental category" for each customer (GROUP BY c.customer_id, just in case we have two customers with the same first and last names) and comparing to the count of category.
SELECT c.last_name
, c.first_name
FROM customer c
JOIN rental r
ON r.customer_id = c.customer_id
JOIN inventory i
ON i.inventory_id = r.inventory_id
JOIN film f
ON f.film_id = i.film_id
GROUP
BY c.last_name
, c.first_name
, c.customer_id
HAVING COUNT(DISTINCT f.category_id)
= (SELECT COUNT(DISTINCT a.category_id) FROM category a)
ORDER
BY c.last_name
, c.first_name
, c.customer_id
EDIT
And here's a demonstration of the other approach, generating a cartesian product of all customers and all categories (WARNING: do NOT do this on LARGE sets!), and find out if any of those rows don't have a match.
-- customers who have rented from EVERY category
-- h = cartesian (cross) product of all customers with all categories
-- g = all categories rented by each customer
-- perform outer join, return all rows from h and matching rows from g
-- if a row from h does not have a "matching" row found in g
-- columns from g will be null, test if any rows have null values from g
SELECT h.last_name
, h.first_name
FROM ( SELECT hi.customer_id
, hi.last_name
, hi.first_name
, hj.category_id
FROM customer hi
CROSS
JOIN category hj
) h
LEFT
JOIN ( SELECT c.customer_id
, f.category_id
FROM customer c
JOIN rental r
ON r.customer_id = c.customer_id
JOIN inventory i
ON i.inventory_id = r.inventory_id
JOIN film f
ON f.film_id = i.film_id
GROUP
BY c.customer_id
, f.category_id
) g
ON g.customer_id = h.customer_id
AND g.category_id = h.category_id
GROUP
BY h.last_name
, h.first_name
, h.customer_id
HAVING MIN(g.category_id IS NOT NULL)
ORDER
BY h.last_name
, h.first_name
, h.customer_id
I will take a stab at this, only because I am curious why the answer proposed seems so complex. First, a couple of questions.
So your question is: "Select the first name and last name of the clients which rent films (that have DVD's) from all the categories, ordering by first name and last name."
So, just go through the rental database, joining customer. I am not sure what the category part has anything to do with this, as you are not selecting or displaying any category, so that does not need to be part of the search, it is implied as when they rent a DVD, that DVD has a category.
SELECT C.first_name, C.last_name
FROM customer as C JOIN rental as R
ON (C.customer_id = R.customer_id)
WHERE R.return_date IS NOT NULL;
So, you are looking for movies that are currently rented, and displaying the first and last names of customers with active rentals.
You can also do some UNIQUE to reduce the number of duplicate customers that show up in the list.
Does this help?!