sql select sum conditions - sql

Question

I'm studying sql (by myself) and I would like to know how I would do for these examples:
1- i'd create this 3 tables bellow:
CREATE TABLE Business (
Id INT,
Category INT,
Business_Name VARCHAR(30),
City_Id INT,
Billing INT
);
INSERT INTO business (Id, Category, Business_Name, City_Id, Billing) VALUES(1, 1, 'Bread', 1, 50);
INSERT INTO business (Id, Category, Business_Name, City_Id, Billing) VALUES(2, 2, 'Oreo', 2, 10);
INSERT INTO business (Id, Category, Business_Name, City_Id, Billing) VALUES(3, 2, 'Pizza', 3, 15);
INSERT INTO business (Id, Category, Business_Name, City_Id, Billing) VALUES(4, 2, 'Beer', 4, 25);
INSERT INTO business (Id, Category, Business_Name, City_Id, Billing) VALUES(5, 1, 'Steak', 1, 80);
CREATE TABLE City (
Id INT,
City_Name VARCHAR(30)
);
INSERT INTO City (Id, City_Name) VALUES(1, 'Paris');
INSERT INTO City (Id, City_Name) VALUES(2, 'New York');
INSERT INTO City (Id, City_Name) VALUES(3, 'Tokio');
INSERT INTO City (Id, City_Name) VALUES(4, 'Vancouver');
INSERT INTO City (Id, City_Name) VALUES(5, 'Cairo');
CREATE TABLE Category (
Id INT,
Category_Name VARCHAR(30)
);
INSERT INTO Category (Id, Category_Name) VALUES(1, 'Bar');
INSERT INTO Category (Id, Category_Name) VALUES(2, 'Pub');
INSERT INTO Category (Id, Category_Name) VALUES(3, 'Pizza');
2- I want to make these SQL queries:
a) Total Value of Billing (Billing) all stores, like this table:
-----------------------
|Business_Name | Total |
|--------------+-------|
|Total | 180 |
------------------------
b) All Total Billing by Category_Name like this table:
-------------------
|Category | Total |
|---------+-------|
|Bar | 130 |
|---------+-------|
|Pub | 50 |
|---------+-------|
|Pizza | 5 |
----------+--------
c)List the Business_Name with min billing, showing the: Category_Name, Business_Name, and Billing like this table:
----------------------------------------
|Category_Name | Business_Name | Total |
|--------------+---------------+-------|
|Pub | Beer | 5 |
|--------------+---------------+--------
d) All Total of Billing by City, showing the: Category_Name, Business_Name, City_Name and Billing like this table
--------------------------
|City | Total |
|----------------+-------|
|Cairo | 0 |
|----------------+-------|
|New York | 10 |
|----------------+-------|
|Paris | 130 |
|----------------+-------|
|Tokio | 15 |
-----------------+--------
|Vancouver | 25 |
-----------------+--------
Any body with a little more knowledge that could be help me, please? =)

Answer 1

First thing is first, all of these are basic queries and i have to point out that a simple google search for tutorials(ex1, ex2, ex3) would have answered most of these. as we are here to provide help and guidance i hope you take it to heart and read the tutorials before going over the answers.
with that said to be able to help you out i will walk through each query and provide an overview of what is happening.
a) you need an aggregate operation here to sum up the values. You would use the sum key word. normally you need a group by, but in this case since we only have a hard coded column with the word "Total" in it, it is not required. we also give each of the columns an alias as per your table. this is after the column name.
select 'Total' as business_Name,
sum(billing) Total
from business
b) This one is almost an exact copy of a, but requires a grouping. in this case you have to use the group by key word for all columns that are not in aggregates. in this case it is only the category name. it is good practice to not use the ordinal position in group by and order by statements, you should always spell out the columns you are using when able.
select c.category_name,
sum(billing) total
from business b
inner join category c
on b.category = c.id
group by c.category_name
c) We continue to build onto the query and add another column in the select statement and then add a column to the group by to allow grouping.
select c.category_name,
b.business_name,
sum(billing) total
from business b
inner join category c
on b.category = c.id
group by c.category_name, b.business_name
d) For this query its very similar to b, but instead of category_name we do a join on city with city id.
select c.city_name
,sum(billing) as total
from business b
inner join city c on c.id = b.city_id
group by c.city_name
with all of this said, several of your examples do not match your expected output. but these queries do match the expected output with the data you provided.
I really do recommend going through some tutorials to grasp the basics of sql better.

Answer 2

Here is answer to one of the queries. But I'd recommend you to read online basic sql tutorials and you will be able to write them yourself easily.
b)
select c.category_name
,sum(billing)
from business b
join category c
on b.category = c.id
group by 1