I have two tables, the first, hotel_info that has fields such as(hotel_id,hotel_name,location) and a second table rooms, that has room information such as(room_id,room_name,hotel_id,rate,description). I want a query that returns the minimum room rate for a hotel and all information about the hotel from the hotel_info table. So far I have this query that is working properly but its not returning the minimum room rate.
SELECT a.hotel_id,a.hotel_name ,a.location, b.rate FROM hotel_info a
LEFT JOIN rooms b ON b.hotel_id=a.hotel_id
GROUP BY hotel_id
How get the minimum room rate per hotel?
You can use the mysql function min() such as
select a.hotel_id, min(b.rate)
from hotel_info a
left join rooms b on b.hotel_id = a.hotel_id
group by a.hotel_id;
SELECT a.hotel_id, a.hotel_name, a.location, min(b.rate) as min_rate
FROM hotel_info a
LEFT JOIN rooms b ON b.hotel_id = a.hotel_id
GROUP BY a.hotel_id, a.hotel_name, a.location
Related
first sorry, i don't have fluid english.
I want select 3 rows in 3 different tables, two of them without Foreing Key/relation.
Need to select amount of customers in each store, and total amount of payments in these stores in one query.
Here are the tables:
Customers
Stores
Payments
I have tried these querys to get payments for each store and customers for each store, but don't know how can unify in one query:
Payments/store
SELECT count(a.payment_id) as alquileres, b.store_id
FROM customer b, payment a
WHERE a.customer_id = b.customer_id
GROUP BY b.store_id;
customers/store
SELECT count(customer_id), store_id
FROM customer
GROUP BY store_id;
But when I add count(customer_id) in unique query don't have same results.
You can use one query:
select c.store_id,
count(distinct c.customer_id) as num_customers,
count(p.payment_id) as num_payments
from customers c left join
payments p
on p.customer_id = c.customer_id
group by c.store_id;
I have the following three tables:
I have Following Query to Join Above 3 Tables
customer.customer_id,
customer.name,
SUM(sales.total),
sales.created_at,
SUM(sales_payments.amount)
FROM
sales INNER JOIN customer ON customer.customer_id = sales.customer_id
INNER JOIN sales_payments ON sales.customer_id = sales_payments.customer_id
WHERE sales.created_at ='2020-04-03'
GROUP By customer.name
Result for Above Query is given below
Sum of sales.total is double of the actual sum of sales.total column which has 2-row count, I need to have the actual SUM of that column, without doubling the SUM of those rows, Thank you, for your help in advance..
PROBLEM
The problem here is that there are consecutive inner joins and the number of rows getting fetched in the second inner join is not restricted. So, as we have not added a condition on sales_payment_id in the join between the sales and sales_payment tables, one row in sales table(for customer_id 2, in this case) would be mapped to 2 rows in the payment table. This causes the same values to be reconsidered.
In other words, the mapping for customer_id 2 between the 3 tables is 1:1:2 rather than 1:1:1.
SOLUTION
Solution 1 : As mentioned by Gordon, you could first aggregate the amount values of the sales_payments table and then aggregate the values in sales table.
Solution 2 : Alternatively (IMHO a better approach), you could add a foreign key between sales and sales_payment tables. For example, the sales_payment_id column of sales_payment table can be introduced in the sales table as well. This would facilitate the join between these tables and reduce additional overheads while querying data.
The query would then look like:
`SELECT c.customer_id,
c.name,
SUM(s.total),
s.created_at,
SUM(sp.amount)
FROM customer c
INNER JOIN sales s
ON c.customer_id = s.customer_id
INNER JOIN sales_payments sp
ON c.customer_id = sp.customer_id
AND s.sales_payments_id = sp.sales_payments_id
WHERE s.created_at ='2020-04-03'
GROUP BY c.customer_id,
c.name,
s.created_at ;`
Hope that helps!
You have multiple rows for sales_payments and sales per customer. You need to pre-aggregate to get the right value:
SELECT c.customer_id, c.name, s.created_at, s.total, sp.amount
FROM customer c JOIN
(SELECT s.customer_id, s.created_at, SUM(s.total) as total
FROM sales s
WHERE s.created_at ='2020-04-03'
GROUP BY s.customer_id, s.created_at
) s
ON c.customer_id = s.customer_id JOIN
(SELECT sp.customer_id, SUM(sp.amount) as amount
FROM sales_payments sp
GROUP BY sp.customer_id
) sp
ON s.customer_id = sp.customer_id
Hi so this is my case I have those tables
Customer {id,name}
Charges {id,amount,customer_id}
Taxes {id,amount,charge_id}
so I want to SUM amount of charges and taxes then group by customer id here is my query
SELECT SUM(ch.amount),SUM(t.amount)
FROM Customer c
LEFT JOIN Charges ch ON ch.customer_id = c.id
LEFT JOIN Taxes t ON t.charge_id = ch.id
GROUP BY c.id;
so in case I have 1 charge for customer than I have 2 taxes for that charge when I use SUM function it's counting amount of charge twice for example in case to show me 10$ it' showing me 20$
I know how can I fix that through subqueries, but I want to know is there any option to get correct value without subqueries like query I use above what can I modify there to fix that.
Thanks !
UPDATED ANSWER WITHOUT SUBQUERIES
SELECT
SUM(CASE WHEN #ch_id != ch.id
THEN ch.amount END) AS ch_amount,
SUM(t.amount) AS t_sum,
c.*,
#ch_id := ch.id
FROM
Customer c
LEFT JOIN charges ch ON c.id = ch.reservation_id
LEFT JOIN taxes t ON ch.id = t.charge_id
GROUP BY rs.id;
You want to know if you can do this without subqueries. No, you can't.
If a row in Charges has more than one corresponding row in Taxes, you can't simply join the tables without duplicating Charges rows. Then, as you have discovered, when you sum them up, you'll get multiple copies.
You need a way to get a virtual table (a subquery) with one row for each Charge.
SELECT ch.customer_id,
ch.amount amount,
tx.tax tax
FROM Charges
LEFT JOIN (
SELECT SUM(amount) tax,
charge_id
FROM Taxes
GROUP BY charge_id
) tx ON ch.id = tx.charge_id
You can then join that subquery to your Customer table to summarize sales by customer.
This is a pain because of the multiple hierarchies. I would suggest:
SELECT c.id, ch.charge_amount, ch.taxes_amount
FROM Customer c LEFT JOIN
(SELECT ch.customer_id, SUM(ch.amount) as charge_amount,
SUM(t.taxes_amount) as taxes_amount
FROM Charges ch LEFT JOIN
(SELECT t.charge_id, SUM(t.amounts) as taxes_amount
FROM taxes t
GROUP BY t.charge_id
) t
ON t.charge_id = ch.id
GROUP BY ch.customer_id
) ch
ON ch.customer_id = c.id;
You are not going to be able to fix this without subqueries of one form or another, if there are multiple charges for a customer or multiple taxes on a charge.
I have 2 MySQL tables (countries) and (reservations)
I want to list every row from countries and simply indicate whether there is a match on reservations or not.
In each instance:
reservations will have 1 matching rows, or
reservations will have many matching rows, or
reservations will have no matching rows
So all I want from the join is to know whether there is a match to reservations or not. Nothing else.
Here is my query statement:
SELECT country.countryID, reservation.citizen
FROM countries AS country
LEFT JOIN (
SELECT reservationID
FROM reservations
LIMIT 1
) AS reservation ON reservation.citizen = country.countryID
ORDER BY reservation.citizen
It fails with Unknown column 'reservation.citizen' in 'on clause'
CONCLUSION:
JOINs cannot solve the problem.
The issue is in the subselect. Notice you have not included the field citizen inside reservation.
SELECT country.countryID, reservation.citizen
FROM countries AS country
LEFT JOIN (
SELECT reservationID, citizen
FROM reservations
LIMIT 1
) AS reservation ON reservation.citizen = country.countryID
ORDER BY reservation.citizen
By the other hand, why are you doing a subselect? And why the limit? Wouldn't be better to just query the following?
SELECT
country.countryID,
count(reservation.reservationID)
FROM
countries AS country
LEFT JOIN reservations AS reservation
ON country.countryID = reservation.citizen
GROUP BY
country.countryID
HAVING
count(reservation.reservationID) > 0
ORDER BY
reservation.citizen
;
You have an issue with the join, it should be like
LEFT JOIN reservations AS reservation ON reservation.citizen = country.countryID
ORDER BY reservation.citizen
OR
LEFT JOIN (
SELECT *
FROM reservations
LIMIT 1
) AS reservation ON reservation.citizen = country.countryID
ORDER BY reservation.citizen
OR better LEFT OUTER JOIN to get rows not matching join conditions.
LEFT OUTER JOIN reservations AS reservation ON reservation.citizen = country.countryID
ORDER BY reservation.citizen
This is my query:
SELECT count(*) as total, dp.name,dp.id,dp.description, dp.avatar
FROM `doctors` d
right join departments dp on d.department_id = dp.id
group by d.department_id
I have to tables: doctors and departments. I want to extract the total number of doctors from each department. This query works fine, it returns me all of the deparments, which have a doctors, but not which does not have. Somehow I want to show all of the departements and a total, which represents the doctors whose belong to a department. How can i do that ?
This is the doctor table:
and this is the departments table
You can give this a try:
SELECT
(SELECT count(*) FROM doctors d WHERE d.department_id = dp.id) AS total,
dp.*
FROM departments AS dp
And if you want to use JOIN then try this:
SELECT
COUNT(d.department_id) AS total,
dp.*
FROM departments AS dp
LEFT JOIN doctors AS d ON dp.id = d.department_id
GROUP BY dp.id
SELECT (SELECT count(*) FROM doctors AS d WHERE d.id = dp.id) as total, dp.name,dp.id,dp.description, dp.avatar
FROM departments dp
there are multiple ways of doing this ofcourse, I would do it like this
i dont think you need to join you just need a count of all the doctors and you dont do anything with the rest of the information
In my couple of decades working with SQL I've never used right joins. I've always found the LEFT join easier to read. I also try and return the columns in order of the highest to lowest level of detail and finish with sum's and counts. It reads a lot better.
Try this:
SELECT dp.id,dp.name,dp.description, dp.avatar,count(*) as total
FROM departments dp
LEFT JOIN doctors d
on d.department_id = dp.id
GROUP BY dp.id,dp.name,dp.description, dp.avatar
You must always group by every column within your select clause except those that are an aggregation (e.g. sum,count) or a constant.