I am building an application to manage an inventory and I have a problem when creating my tables for the database (I am using PostgreSQL). My problem is the following:
I have two tables, one called 'products' and one called 'users'. Each one with its columns (See image). I want to create a third table called 'product_act_register' , which will keep a record of activity of the products and has with it the columns id, activity_type, quantity, date. But, I want to add other columns which are taken from the table 'users' and 'products'.
It should look like this (Image)
Where product_id, product_name, product_category, product_unit are taken from the table 'products' and the column 'user_id' is taken from the table 'users'.
How can I do this with PostgreSQL ?
Your description and your precise goals are very unclear. You didn't tell us what should happen in the different cases (only a product exists or only a user exists or none exist or both exist). You also didn't tell us how the other columns not coming from these tables should be filled. You furthermore didn't tell us how the tables users and products depend on each other. Basically you con do something like this if you only want to do an insert if both tables have an entry:
INSERT INTO product_acts_register
SELECT 1,'ActivityType1',p.id, p.name, p.category,
p.unit, u.id, 100, CURRENT_DATE
FROM products p JOIN users u ON p.id = u.id;
(Since you didn't tell us how or if to join them, I assumed to join on their id column)
If you don't care about this, but want to insert an entry for any possible combination of users and products, you can just select both tables without joining:
INSERT INTO product_acts_register
SELECT 1,'ActivityType1',p.id, p.name, p.category,
p.unit, u.id, 100, CURRENT_DATE
FROM products p, users u;
You can replicate this here and try out other commands: db<>fiddle
Please be more precise and give us more information when asking the next question.
Related
Hi guys I'm new with databases and I'm trying to make a query where I join 3 tables. I could make it and I want to clean up the result. I want to know how can I delete the column "pin" from users table and maybe some "ids" columns.
Select * from "wish-list"
Join products
On "wish-list".id = products.holiday_id
Join users
On "wish-list".user_id = users.id
Where "wish-list".id = 1
You need to specify which columns you really need in your output. At the moment you are using
SELECT * which outputs all columns of all joined tables.
Here is what it should look like:
SELECT holiday, products.description, users.pin FROM "wish-list"
JOIN products ON "wish-list".id = products.holiday_id
JOIN users ON "wish-list".user_id = users.id
WHERE "wish-list".id = 1
It's important that you reference all columns which are not your main entity (here wish-list) with tablename.column (products.description and not only description). It will work without referencing strictly but only if the column name is unique in your query.
Furthermore you can rename columns. This is useful for example if you want to get the id's of the product table and the wish-list table.
SELECT product.id AS product_id, id AS wishlist_id FROM "wish-list"
...
Hope that helps!
I need to brind a lot of columns from several tables using LEFT JOIN. My starting point is the orders table and I bring the vendor name from the "Address_table". Then I add another table with order details and then the shipping information of each order detail.
My problem is that I need to bring a different record from "Address_table" to refer onether id's detailed in shipment table as of "origin_id" and "destination_id".
In other words, "address_id", "origin_id" and "destination_id" are all records from "Address_table". I brought the first one related to the vendor, how can I retrieve the other two?
Example
Thanks in advance
Your question is not exactly clear in terms of the tables and their relationships. It is, however, clear what the problem is. You need to join against the same table twice using different columns.
In order to do that you need to use table aliases. For example, you can do:
select *
from shipment s
left join address_table a on a.address_id = s.origin_id
left join address_table b on b.address_id = s.destination_id
In this example the table address_table is joined twice against the table shipment; the first time we use a as an alias, the second time b. This way you can differentiate how to pick the right columns and make the joins work as you need them to.
CREATE TABLE users
()
CREATE TABLE avatars
()
CREATE TABLE weapons
()
I need two queries for these tables that I created and I am having trouble doing it, any help would be greatly appreciated.
For all Avatars produce a list showing the avatar name, the total number of weapons it currently holds and the total cost of all weapons currently held. I want no more extra information shown apart from these three main pieces, so I need to get information from table 2 and 3.
For any given User email (i.e. entered at runtime) list the owned Avatar names in reverse order of date of birth and the weapons (including weapon name, range and cost) held by that Avatar.
Any help would be greatly appreciated. I am using SQL*Plus. The tables are not very efficient so any improvements would be welcomed but mainly I need help with these queries.
select
max(a.name),
count(1),
sum(w.cost)
from
avatars a
inner join weapons w on w.weapon_id=a.no_wp_id
group by
a.no_wp_id
;
select
a.name,
w.weapon_name,
w.range,
w.cost
from
users u
inner join avatars a on a.user_id=u.id
inner join weapons w on w.weapon_id=a.no_wp_id
where
u.email='given#email.com'
order by
a.dateOfBirth desc
;
If your queries depend on email being unique, you should have a unique key on it.
Your weapons table does not appear to have a range column on it, but you implied it does in your requirement for query #2. I've included w.range anyway.
In avatars, no_wp_id should probably be named something like avatar_id or just id, and in weapons, weapon_id should be named avatar_id.
You should go through an SQL tutorial. Here's one: http://www.tutorialspoint.com/sql/sql-overview.htm.
I'm currently working on a personal project and I could use a little help. Here's the scenario:
I'm creating a database (MS Access) for all of the movies myself and some friends have ever watched. We rated all of our movies on IMDb and used the export feature to get all of the movie data and our movie ratings. I plan on doing some summary analysis on Excel. One thing I am interested in is the most common movie genre that each person watched. Below is my current scenario. Note that the column "const" is the movies' unique IDs. I also have individual tables for each person's ratings and the following tables are the summary tables that make up the combination of all the movies we have watched.
Here's the table I had: http://imgur.com/v5x9Dhg
I assigned each genre an ID, like this: http://imgur.com/aXdr9XI
And here is a table where I have separate instances for each movie ID and a unique genre: http://imgur.com/N0wULo8
I want to find a way to count up all of the genres that each person watches. Any advice? I would love to provide any additional information that you need!
Thank you!
You need to have at least one table which has one row per user and const (movie watched). In the 3 example tables you posted nothing shows who watched which movies, which is information you need to solve your problem. You mention having "individual tables for each person's ratings," so I assume you have that information. You will want to combine all of them though, into a table called PERSON_MOVIE or something of the like.
So let's say your second table is called GENRE and its columns are ID, Genre.
Let's say your third table is called GENRE_MOVIE and its columns are Const and ID (ID corresponds to ID on the GENRE table)
Let's say the fourth table, which you did not post, but which is required, is called PERSON_MOVIE and its columns are person, Const, rating.
You could then write a query like this:
select vw1.*, ge.genre
from (select um.person, gm.id as genre_id, count(*) as num_of_genre
from user_movie um
inner join genre_movie gm
on um.const = gm.const
group by um.person, gm.id) vw1
inner join (select person, max(num_of_genre) as high_count
from (select um.person, gm.id, count(*) as num_of_genre
from user_movie um
inner join genre_movie gm
on um.const = gm.const
group by um.person, gm.id) x
group by person) vw2
on vw1.person = vw2.person
and vw1.num_of_genre = vw2.high_count
inner join genre ge
on vw1.genre_id = ge.id
Edit re: your comment:
So right now you have multiple tables reflecting people's ratings of movies. You need to combine those into a table called PERSON_MOVIE or something similar (as in example above).
There will be 3 columns on the table: person, const, rating
I'm not sure if access supports the traditional create table as select query but ordinarily you would be able to construct such a table in the following way:
create table person_movie as
select 'Bob', const, [You rated]
from ratings_by_bob
union all
select 'Sally', const, [You rated]
from ratings_by_sally
union all
select 'Jack', const, [You rated]
from ratings_by_jack
....
If not, just combine the tables manually and add a third column as shown indicating what users are reflected by each row. Then you can run my initial query.
I am having trouble with writing a SQL query in Access with foreign keys. There are two tables, 'Customers'(ID, Name, Surname) and 'Orders'(ID, Customer, Date, Volume). ID fields are primary, and Orders.Customer is a foreign key linked to Customers.ID, so a customer can have many orders or none.
My goal is to do a search on customers based on many criteria, one of which being if customers have at least an order which volume is superior to a certain quantity. I tried joins with SELECT DISTINCT but it still gives me duplicate results, plus I had to create an empty order for every customer without orders if the query didn't use the above condition.
Does anyone have an idea about that? Maybe some special instruction on foreign keys or 2 separate queries?
Based on the information you give, i only can give you hints on what I think you're doing/understanding wrong :
SELECT DISTINCT does select you a unique record, not a unique value, so if your statement selects all fields (*), distinct won't help you much there.
My guess is you had to create an empty order for each customer because you used INNER JOIN, try LEFT OUTER JOIN instead
For example :
SELECT DISTINCT Customers.*
FROM Customers
LEFT OUTER JOIN Orders
ON (Orders.Customer = Customers.id)
WHERE Volume > put_your_value