I created the following tables:
create table people (
ID varchar(9),
name varchar(20),
CONSTRAINT pk_ID PRIMARY KEY (ID)
);
create table cars (
license_plate varchar(9),
ID varchar(9),
CONSTRAINT pk_ID PRIMARY KEY (license_plate)
);
create table accidents (
code varchar(9),
license_plate varchar(9),
CONSTRAINT pk_ID PRIMARY KEY (code)
);
I inserted the following data:
insert into people(ID, name) values('0x1','Louis');
insert into people(ID, name) values('0x2','Alice');
insert into people(ID, name) values('0x3','Peter');
insert into cars(license_plate, ID) values('001','0x1');
insert into cars(license_plate, ID) values('002','0x2');
insert into cars(license_plate, ID) values('003','0x1');
insert into cars(license_plate, ID) values('004','0x3');
insert into accidents(code, license_plate) values('fd1','001');
insert into accidents(code, license_plate) values('fd2','004');
insert into accidents(code, license_plate) values('fd3','002');
The question is: How to select people who don't have had accidents in any of their cars?
My problem is that when I was trying to use not in. Having "Louis" at least one car in the table accidents, the query show me "Louis"and should not show "Louis".
My query:
select ID from people where ID in (select ID from cars where license_plate not in (select license_plate from accidents));
Result:
+-----+
| ID |
+-----+
| 0x1 |
+-----+
select name from people where ID not in (
select distinct c.ID from
accidents as a inner join cars as c
on a.license_plate = c.license_plate
)
Explanation = the sub query will join the cars and accidents, will give you the ID's of all cars who had accidents. On this you can run not in query on the people table
I need two subquery
select id from people
where id not it
(select id form cars where licens_plate not in
(select distintc license_plate from accidents))
This should be quite fast:
SELECT people.* FROM people
LEFT JOIN cars ON cars.ID = people.ID
LEFT JOIN accidents ON accidents.license_plate = cars.license_plate
WHERE accidents.code IS NULL
GROUP BY people.ID
Related
I have a problem, I've spent a lot of time on. I have to display the pairs of items (Item1, Item2, How many) that appear on the invoices - and how many pairs have repeated. The table that connects invoices to goods is called "Transactions".
I Have 3 tables:
Items: IdItem, Name
Transactions: IdTransaction, IdInvoice, IdItem
Invoices: IdInvoice
Result of SQL Query must be:
Item1 | Item2 | Number
This sounds like a self-join and aggregation:
select t1.IdItem as IdItem1, t2.IdItem as IdItem2, count(*)
from transactions t1 join
transactions t2
on t1.IdInvoice = t2.IdInvoice and
t1.IdItem < t2.IdItem
group by t1.IdItem, t2.IdItem
order by count(*) desc;
Assuming your tables look like this:
CREATE TABLE Items (
IDItem INT,
Name VARCHAR,
PRIMARY KEY(IDItem)
);
CREATE TABLE Invoices (
IDInvoice INT,
PRIMARY KEY(IDInvoice)
);
CREATE TABLE Transactions (
IDTransaction INT,
IDInvoice INT,
IDItem INT,
PRIMARY KEY(IDTransaction),
FOREIGN KEY (IDItem) REFERENCES Items(IDItem),
FOREIGN KEY (IDInvoices) REFERENCES Invoices(IDInvoices)
)
If this is true then you need to query the results like this:
SELECT i.Name,in.IDInvoice FROM Transactions t
JOIN Items i ON i.IDItem = t.IDItem
JOIN Invoices in ON in.IDInvoice = t.IDInvoice
WHERE i.Name = item1
I have two tables, student_records and subjects. I have to find out those students who have taken all the subjects (1,2,3) from the subjects table.
create table subject (ID int primary key, subject varchar(50));
insert into subject values (1,'English'),(2,'Bengali'),(3,'Math');
create table student_records(ID int primary key,student_id int , sub_id int,foreign key (sub_id)
references subject(ID));
insert into student_records values (1,1,1),(2,3,2),(3,1,3),(4,1,2),(5,2,1),(6,3,3),(7,3,1),(8,4,1);
/*select *from student_records;
select *from subject;*/
I have done with this
select student_id from student_records
group by student_id
having count(*)=(select count(*) from subject);
Is there any better query?
Not a "better" way, but I would make sure to use count distinct in this case:
SELECT
student_id
,COUNT( distinct sub_id) AS subject_cnt
FROM student_records
GROUP BY student_id
HAVING subject_cnt = SELECT COUNT(*) FROM subject
When execute my query i just get 1 item back that i attached to the sellerId instead of 2. Does anyone know how i can say?
select the name of item and re seller for each item that belongs to the re seller. With a rating higher than 4?
Current Query:
SELECT items.name, sellers.name
FROM items
inner JOIN sellers
on items.id=sellers.id
WHERE rating > 4
ORDER BY sellerId
The query for tables inc. data:
CREATE TABLE sellers (
id INTEGER NOT NULL PRIMARY KEY,
name VARCHAR(30) NOT NULL,
rating INTEGER NOT NULL
);
CREATE TABLE items (
id INTEGER NOT NULL PRIMARY KEY,
name VARCHAR(30) NOT NULL,
sellerId INTEGER REFERENCES sellers(id)
);
INSERT INTO sellers(id, name, rating) values(1, 'Roger', 3);
INSERT INTO sellers(id, name, rating) values(2, 'Penny', 5);
INSERT INTO items(id, name, sellerId) values(1, 'Notebook', 2);
INSERT INTO items(id, name, sellerId) values(2, 'Stapler', 1);
INSERT INTO items(id, name, sellerId) values(3, 'Pencil', 2);
You've got the wrong join, here's a corrected query;
SELECT items.name, sellers.name
FROM items
inner JOIN sellers
on items.sellerId=sellers.id
WHERE rating > 4
ORDER BY sellerId
You're joining on id = id, you want sellerid = id
Notice in your table definition that item.sellerId is the field that joins to seller.id
CREATE TABLE items (
id INTEGER NOT NULL PRIMARY KEY,
name VARCHAR(30) NOT NULL,
sellerId INTEGER REFERENCES sellers(id)
);
You need to join on the correct column:
SELECT i.name, s.name
FROM items i INNER JOIN
sellers s
ON i.sellerid = s.id
----------^
WHERE rating > 4
ORDER BY i.sellerId
Note that I also introduced table aliases and qualified column names. These make a query easier to write and to read.
SELECT items.name, sellers.name
FROM items, sellers
WHERE items.sellerId = sellers.id and sellers.rating>4;
Here is the right query:
SELECT items.name as items, sellers.name as sellers
FROM sellers
INNER JOIN items
ON (sellers.id = items.sellerid)
WHERE sellers.rating > 4
Database description
I have a simple database composed of three tables: customer, product and custumer_product.
customer: Contains the information about the customer. His ID and name
product: Contains informations about the products that are available in the store. ID and name
custumer_product: junction table
- customer (table)
id integer primary key not null
name TEXT
- custumer_product (table)
id_product integer
id_customer integer
primary key(id_product, id_customer)
FOREIGN KEY(Id_product) REFERENCES product(id)
FOREIGN KEY (ID_customer) REFERENCES customer(ID)
- product (table)
id integer primary key not null
name TEXT
The three tables have been initialized in sqlfiddle by using SQLITE. The following SQL queries are used to construct the database
create table if not exists customer (id integer primary key not null, name TEXT);
create table if not exists product (id integer primary key not null, name TEXT);
create table if not exists customer_product (id_product integer, id_customer
integer, primary key(id_product, id_customer), FOREIGN KEY(Id_product) REFERENCES product(id), FOREIGN KEY (ID_customer) REFERENCES customer(ID));
insert into customer(id,name) values(1,"john");
insert into customer(id,name) values(2,"Paul");
insert into customer(id,name) values(3,"Jenny");
insert into customer(id,name) values(4,"Fred");
insert into customer(id,name) values(5,"Lea");
insert into product(id,name) values(1,"Mouse");
insert into product(id,name) values(2,"screen");
insert into product(id,name) values(3,"pc");
insert into product(id,name) values(4,"CD");
insert into product(id,name) values(5,"Game");
insert into customer_product values(1,1);
insert into customer_product values(1,2);
insert into customer_product values(1,3);
insert into customer_product values(2,1);
insert into customer_product values(2,2);
insert into customer_product values(2,3);
insert into customer_product values(3,4);
insert into customer_product values(4,5);
insert into customer_product values(5,5);
Problem
For every customer I want to select all the other customers that bought at least one similar product.
John and Paul bought at least 1 similar product
No customer bought a similar product as jenny yet
Fred and lea bought a similar product
output
"John" "Paul"
"Jenny"
"Fred" "Lea"
This is basically a self-join and possibly an aggregation. For instance, the following gets all customers that have purchased a similar product as another, ordered by the number of similar products:
select cp.id_customer, cp2.id_customer, count(*)
from customer_product cp join
customer_product cp2
on cp.id_product = cp2.id_product
group by cp.id_customer, cp2.id_customer
order by cp.id_customer, count(*) desc;
You can bring in additional information such as customer names by doing additional joins.
While I'm not entirely sure I understand the conditions, there are three basic steps to this problem, which you can combine into one query (or not).
Get the products that the customer bought
Get the IDs of the customers that bought the same products
Get the customer details based on those IDs
So for 1, you do a simple select:
SELECT id_product FROM customer_product WHERE id_customer = 1
For 2, you can use the IN statement:
SELECT * FROM customer_product WHERE id_product IN
(SELECT id_product FROM customer_product WHERE id_customer = 1);
For 3 use a combination of JOIN and GROUP BY to get the relevant details from the customer table.
first find the list of product bought by at least 2 customers, second find the name of the custumers using the join table and third select the customer's name once. here is the query:
select distinct c.name from(select c.name, p.name,cp.id_customer, cp.id_product from customer_product cp join customer c on c.id=cp.id_customer join product p on p.id=cp.id_customer where cp.id_product in(select id_product, total from(select id_product,count(*) as total from customer_product group by id_product)p where total>=2)p1)p2)
I have two tables, a for access and p for provider. I then have third table for joining the tables together, standard normalization. However, the provider table is a parent/child table, and the joining table has an option whether the access should be granted for all the provider children or not.
CREATE TABLE p (
p_id int PRIMARY KEY,
name varchar(32),
parent_id int,
FOREIGN KEY (parent_id) REFERENCES p(p_id)
);
CREATE TABLE a (
a_id int PRIMARY KEY,
name varchar(32)
);
CREATE TABLE ap (
a_id int,
p_id int,
sub tinyint,
FOREIGN KEY (a_id) REFERENCES a(a_id),
FOREIGN KEY (p_id) REFERENCES p(p_id)
);
Some sample data, 1 provider with 2 child providers. 2 access users, 1 with no child access and with child access.
INSERT INTO p VALUES(1, 'a', null);
INSERT INTO p VALUES(2, 'a.a', 1);
INSERT INTO p VALUES(3, 'a.b', 1);
INSERT INTO a VALUES(1, 'user 1');
INSERT INTO a VALUES(2, 'user 2');
INSERT INTO ap VALUES(1, 1, 0);
INSERT INTO ap VALUES(2, 1, 1);
The result is that I want to have a list of providers that the user have access to, based on the third table.
Currently I've solved this by joining two queries with UNION. The first query selects possible child providers and the second goes for primary providers.
SELECT p_id, name
FROM p
WHERE parent_id IN(
SELECT p_id FROM ap WHERE a_id = 1 AND sub = 1
)
UNION
SELECT ap.p_id, p.name
FROM ap
LEFT JOIN p ON p.p_id = ap.p_id
WHERE a_id = 1;
I don't like this query, it's ugly and there must be a smarter way :)
If I have the logic correct, then you want all records from p where one of the following is true:
p_id matches a record in ap for the given a_id.
parent_id matches a record in ap for a given a_id.
This suggests using exists for the conditions:
select p.p_id, p.name
from p
where exists (select 1
from ap
where ap.p_id = p.p_id and ap.a_id = 1
) or
exists (select 1
from ap
where ap.p_id = p.parent_id and ap.sub = 1 and ap.a_id = 1
)
With a composite index on ap(p_id, a_id, sub), this should have much better performance than your version of the query.