I have 2 tables
Timetable :
pupil_id, staff_id, subject, lesson_id
Staff_info :
staff_id, surname
The timetable table contains 1000s of rows because each student's ID is listed under each period they do.
I want to list all the teacher's names, and the number of lessons they do (count). So I have to do SELECT with DISTINCT.
SELECT DISTINCT TIMETABLE.STAFF_ID,
COUNT(TIMETABLE.LESSON_ID),
STAFF.SURNAME
FROM STAFF
INNER JOIN TIMETABLE ON TIMETABLE.STAFF_ID = STAFF.STAFF_ID
GROUP BY TIMETABLE.STAFF_ID
However I get the error:
Column 'STAFF.SURNAME' is invalid in the select list because it is not
contained in either an aggregate function or the GROUP BY clause.
This should do what you want:
SELECT s.STAFF_ID, COUNT(tt.LESSON_ID),
s.SURNAME
FROM STAFF s INNER JOIN
TIMETABLE tt
ON tt.STAFF_ID = s.STAFF_ID
GROUP BY s.STAFF_ID, s.SURNAME;
Notes:
You don't need DISTINCT unless there are duplicates in either table. That seems unlikely with this data structure, but if a staff member could have two of the same lesson, you would use COUNT(DISTINCT tt.LESSON_ID).
Table aliases make the query easier to write and to read.
You should include STAFF.SURNAME in the GROUP BY as well as the id.
I have a preference for taking the STAFF_ID column from the table where it is the primary key.
If you wanted staff with no lessons, you would change the INNER JOIN to LEFT JOIN.
SELECT T.STAFF_ID,
T.CNT,
S.SURNAME
FROM STAFF S
JOIN (
SELECT STAFF_ID, CNT = COUNT(/*DISTINCT*/ LESSON_ID)
FROM TIMETABLE
GROUP BY STAFF_ID
) T ON T.STAFF_ID = S.STAFF_ID
Another option:
SELECT DISTINCT si.staff_id, surname, COUNT(lesson_id) OVER(PARTITION BY staff_Id)
FROM Staff_info si
INNER JOIN Timetable tt ON si.staff_id = tt.staff_id
When using Aggregate function(Count, Sum, Min, Max, Avg) in the Select column's list, any other columns that are in the Select column's list but not in a aggregate function, should be mentioned in GROUP BY section too. So you need to change your query as follow and add STAFF.SURNAME to GROUP BY section too:
SELECT TIMETABLE.STAFF_ID,
COUNT(TIMETABLE.LESSON_ID),
STAFF.SURNAME
FROM STAFF
INNER JOIN TIMETABLE ON TIMETABLE.STAFF_ID = STAFF.STAFF_ID
GROUP BY TIMETABLE.STAFF_ID,STAFF.SURNAME
Distinct is useless also in your scenario. and also as you are going to show the teachers name and Count lessons, you do not need to add TIMETABLE.STAFF_ID to Select's column's list,, but it should remain in Group By section to prevent duplicate names.
SELECT COUNT(TIMETABLE.LESSON_ID),
STAFF.SURNAME
FROM STAFF
INNER JOIN TIMETABLE ON TIMETABLE.STAFF_ID = STAFF.STAFF_ID
GROUP BY TIMETABLE.STAFF_ID,STAFF.SURNAME
You may need to take a look at this W3C post for more info
Related
I have a table and want to calculate the percentage of total by store_id which each (category_id, store_id) subtotal represents. My code is below:
WITH
example_table (name, store_id)
AS
(
select name, store_id
from category
join film_category using (category_id)
join film using (film_id)
join inventory using (film_id)
join rental using (inventory_id)
)
SELECT name, store_id, cast(count(*) as numeric)/(SELECT count(*) FROM example_table)
FROM example_table
GROUP BY name, store_id
ORDER BY name, store_id
This code actually works, as in, it doesn't throw an error, only they're not the results I'm looking for. Here each of the subtotals is divided by the total across both stores and all 16 names. Instead, I want the subtotals divided by their respective store totals or divided by their respective name totals.
I'm wondering how to perform calculations on those subtotals in general.
Thanks in advance,
I believe you need to explore the possibilities of using aggregate functions combined with an OVER(PARTITION BY ...) e.g.
SELECT DISTINCT
name, store_id, store_id_count, name_count
FROM (
select name, store_id
, count(*) over(partition by store_id) as store_id_count
, count(*) over(partition by name) as name_count
from category
join film_category using (category_id)
join film using (film_id)
join inventory using (film_id)
join rental using (inventory_id)
) AS example_table
When using aggregate function with the over clause you get the wanted counts on each row of the result, and it seems that in this case you need this. Note that select distinct has been used simply to reduce the final number of rows returned, you might still need to use a group by but I am not sure if you do.
Once you have the needed values within the derived table (aliases as example_table) then it should be a simple matter of some arithmetic in the overall select clause.
I'm automating a process at work where the output needs to be in a certain non-alphabetical order depending on a name (internal_product, type text) in addition to a number (type text). First I'm running a subquery where I collect information from four slightly different tables using joins. I then append the result with a union before the outer group by sums units and amounts. The pseudo-query is as follows:
select name, number, internal_product, sum(units), sum(amount) from (
select fields, sum(x)
from t1
join join-conditions
join join-conditions
group by name, number, internal_product
union
.....
select fields, sum(x)
from t5
join join-conditions
join join-conditions
group by name, number, internal_product
) as foo
group by name, number, internal_product
order by number, name;
I tried to change a column in a helper table used in one of the joins to an enum type since it is used in the outer group by (SO-thread) but the column type of course needs to be the same in the join-condition so the modified query was not valid. There are 30 product names so I would like to avoid using a CASE name as suggested by gbn and Guffa.
Are there other ways to apply a certain order in a order by?
It might be overkill or complicated for your case, but you could create a custom collation in postgres to sort the way you want. Have a look at the documentation.
https://www.postgresql.org/docs/11/collation.html
I have 3 tables users, orders and comments every tables has 10087250,24949600 and 26532000 much records, I made this query to counts comments on every order but it is taking more than half an hour to execute, how to speed up this query.
Note: there is already index on foreig_key columns.
select users.user_name, orders.id, count(comments.order_id)
from orders
inner join users on users.id=orders.user_id
inner join comments on orders.id=comments.order_id
group by comments.order_id, users.user_name, orders.id
limit 2;
For the first - probably yuo need ORDER BY clause to use it with LIMIT
If you need most commented pair you can ORDER BY count DESC
The second things comments.order_id = orders.id. Why do you use both for GROUP?
group by comments.order_id, users.user_name, orders.id
May be you can help something like this:
WITH grouped AS (
SELECT order_id AS id, count(*)
FROM comments
GROUP BY 1
ORDER BY 2 DESC
LIMIT 2
)
SELECT u.user_name, g.id, g.count
FROM grouped AS g
JOIN orders AS o ON
o.id = g.id
JOIN users AS u ON
u.id = o.user_id
This allows to avoid join all tables before filtering and grouping
You can try to use temporary tables before aggregating the records. This might help to reduce the query time. Something like this...
CREATE TEMPORARY TABLE temp_table(
...
);
INSERT INTO temp_table
SELECT users.user_name, orders.id, comments.order_id
FROM orders INNER JOIN users ON users.id = orders.user_id INNER JOIN comments ON orders.id = comments.order_id;
SELECT user_name, id, count(order_id) FROM temp_table group by order_id, user_name, id;
I think you need to reduce a unneccessary join between orders and comments tables. All you want to get from table comments is how many comments of an order, so you need to do denormalization.
It means you need to add a comments_count column into orders table, and when every a comment is added to an order, just increase it or decrease it if a comment of order is deleted.
After you add new comments_count column, you need to update comments_count for each order.
Then you can just load orders table and you already have comments count for each order.
I have written the following code that counts how many instances of each book_id there are in the table soldBooks.
SELECT book_id, sum(counter) AS no_of_books_sold, sum(retail_price) AS generated_revenue
FROM(
SELECT book_id,1 AS counter, retail_price
FROM shipments
LEFT JOIN editions ON (shipments.isbn = editions.isbn)
LEFT JOIN stock ON (shipments.isbn = stock.isbn)
) AS soldBooks
GROUP BY book_id
As you can see, I used a "counter" in order to solve my problem. But I am sure there must be a better, more built in way of achieving the same result! There must be some way to group a table together by a given attribute, and to create a new column displaying the count of EACH attribute. Can somebody share this with me?
Thanks!
SELECT book_id,
COUNT(book_id) AS no_books_sold,
SUM(retail_price) AS gen_rev
FROM shipments
JOIN editions ON (shipments.isbn=editions.isbn)
JOIN stock ON (shipments.isbn=stock.isbn)
GROUP BY book_id
I'm working on a query that will eventually be used as the record source for a report.
I have a customers and orders table. I want to show customer_id, order_id, and order_date in a query, but I only want to show data associated with the earliest order date for each customer. Basically, I need to show the order_id field without including it in the group by clause. If I include it in the group by clause, I get a lot more records than I want. Based on my research, the code below will work in mysql, but not ms access.
Select customer.customer_id, order.order_id, min(order.order_dt)
From customer inner join order on customer.customer_id = order.customer_id
Group by customer.customer_id
I've tried grouping by order_id in a sub query and ordering by customer then date, then using the first function in the outer query. Unfortunately, the first function doesn't work as advertised.
Any help is greatly appreciated!
Does this work for you? It should bring up the earliest orders by order date for each customer. If there is more than one order on the earliest order date for a customer, all of those orders will be shown, though, so keep it in mind.
SELECT c.customer_id, o.order_id, o.order_dt
FROM customers AS c INNER JOIN (orders AS o INNER JOIN (SELECT customer_ID, MIN([order_dt]) AS MinOrder_dt FROM Orders GROUP BY customer_id) AS d ON (o.Customer_ID = d.customer_id) AND (o.[order_dt] = d.MinOrder_dt)) ON c.customer_id = o.customer_id;
I am deriving a table with just the customer_id and the min order_dt and joining customers and orders to that to only bring up the oldest orders.