I would like to generate a list of all days where every sailor booked a boat in that particular day.
The table scheme is as follows:
CREATE TABLE SAILOR(
SID INTEGER NOT NULL,
NAME VARCHAR(50) NOT NULL,
RATING INTEGER NOT NULL,
AGE FLOAT NOT NULL,
PRIMARY KEY(SID)
);
CREATE TABLE BOAT(
BID INTEGER NOT NULL,
NAME VARCHAR(50) NOT NULL,
COLOR VARCHAR(50) NOT NULL,
PRIMARY KEY(BID)
);
CREATE TABLE RESERVE (
SID INTEGER NOT NULL REFERENCES SAILOR(SID),
BID INTEGER NOT NULL REFERENCES BOAT(BID),
DAY DATE NOT NULL,
PRIMARY KEY(SID, BID, DAY));
The data is as follows:
INSERT INTO SAILOR(SID, NAME, RATING, AGE)
VALUES
(64, 'Horatio', 7, 35.0),
(74, 'Horatio', 9, 35.0);
INSERT INTO BOAT(BID, NAME, COLOR)
VALUES
(101, 'Interlake', 'blue'),
(102, 'Interlake', 'red'),
(103, 'Clipper', 'green'),
(104, 'Marine', 'red');
INSERT INTO RESERVE(SID, BID, DAY)
VALUES+
(64, 101, '09/05/98'),
(64, 102, '09/08/98'),
(74, 103, '09/08/98');
I have tried using this code:
SELECT DAY
FROM RESERVE R
WHERE NOT EXISTS (
SELECT SID
FROM SAILOR S
EXCEPT
SELECT S.SID
FROM SAILOR S, RESERVE R
WHERE S.SID = R.SID)
GROUP BY DAY;
but it returns a list of all days, no exception. The only day that it should return is "09/08/98". How do I solve this?
I would phrase your query as:
SELECT r.DAY
FROM RESERVE r
GROUP BY r.DAY
HAVING COUNT(DISTINCT r.SID) = (SELECT COUNT(*) FROM SAILOR);
Demo
The above query says to return any day in the RESERVE table whose distinct SID sailor count matches the count of every sailor.
This assumes that SID sailor entries in the RESERVE table would only be made with sailors that actually appear in the SAILOR table. This seems reasonable, and can be enforced using primary/foreign key relationships between the two tables.
Taking a slightly different approach of just counting unique sailors per day:
SELECT day FROM (
SELECT COUNT(DISTINCT sid), day FROM reserve GROUP BY day
) AS sailors_per_day
WHERE count = (SELECT COUNT(*) FROM sailor);
+------------+
| day |
|------------|
| 1998-09-08 |
+------------+
Related
I have table company_representatives which looks like that:
Create table script:
CREATE TABLE IF NOT EXISTS company_representatives (
_id integer NOT NULL,
name varchar(50) NOT NULL,
surname varchar(100) NOT NULL,
date_of_join date NOT NULL,
role varchar(250) NOT NULL,
company_id integer NOT NULL,
CONSTRAINT PK_company_representatives PRIMARY KEY ( _id ),
CONSTRAINT FK_144 FOREIGN KEY ( company_id ) REFERENCES companies ( _id )
);
INSERT INTO company_representatives VALUES
(1,'random name','random surname', '2001-01-23', 'CEO', 1),
(2,'next random name','next random surname', '2001-01-23', 'Co-founder', 1),
(3,'John','Doe', '2003-02-12', 'HR', 1),
(4,'Bread','Pitt', '2001-01-23', 'Security officer', 1),
(5,'Toast','Malone', '1997-11-05', 'CEO', 2),
...
I need to pivot this table to make it's columns look like that:
company_id | CEO | Co-Founder | HR | Security Officer
1 1 2 3 4 "_id of company's representatives"
2 5 6 7 8
3 9 10 11 12
You can simply use FILTER directly in the SELECT clause:
SELECT DISTINCT ON (company_id)
company_id,
count(*) FILTER (WHERE role = 'CEO') AS CEO,
count(*) FILTER (WHERE role = 'Co-founder') AS "Co-Founder",
count(*) FILTER (WHERE role = 'HR') AS HR,
count(*) FILTER (WHERE role = 'Security officer') AS "Security Officer"
FROM company_representatives
GROUP BY company_id;
In question it is not clear what the values attached to the roles actually mean, so I assumed you just want to count them. If not, just change it to other aggregate function.
EDIT (see comments): pivot table using crosstab, assuming there is one record for each role in all companies:
SELECT *
FROM crosstab(
'SELECT company_id, _id, name
FROM company_representatives ORDER BY company_id,role'
) AS ct(company_id integer,ceo text,co_founder text,hr text,security_officer text);
Demo: db<>fiddle
Need to find out why my group by count query is not working. I am using Microsoft SQL Server and there are 2 tables I am trying to join.
My query needs to bring up the number of transactions made for each type of vehicle. The output of the query needs to have a separate row for each type of vehicle such as ute, hatch, sedan, etc.
CREATE TABLE vehicle
(
vid INT PRIMARY KEY,
type VARCHAR(30) NOT NULL,
year SMALLINT NOT NULL,
price DECIMAL(10, 2) NOT NULL,
);
INSERT INTO vehicle
VALUES (1, 'Sedan', 2020, 240)
CREATE TABLE purchase
(
pid INT PRIMARY KEY,
vid INT REFERENCES vehicle(vid),
pdate DATE NOT NULL,
datepickup DATE NOT NULL,
datereturn DATE NOT NULL,
);
INSERT INTO purchase
VALUES (1, 1, '2020-07-12', '2020-08-21', '2020-08-23')
I have about 10 rows on information in each table I just haven't written it out.
This is what I wrote but it doesn't return the correct number of transactions for each type of car.
SELECT
vehicle.vid,
COUNT(purchase.pid) AS NumberOfTransactions
FROM
purchase
JOIN
vehicle ON vehicle.vid = purchase.pid
GROUP BY
vehicle.type;
Any help would be appreciated. Thanks.
Your GROUP BY and SELECT columns are inconsistent. You should write the query like this:
SELECT v.Type, COUNT(*) AS NumPurchases
FROM Purchase p JOIN
Vehicle v
ON v.vID = p.pID
GROUP BY v.Type;
Note the use of table aliases so the query is easier to write and read.
If this doesn't produce the expected values, you will need to provide sample data and desired results to make it clear what the data really looks like and what you expect.
I was practicing on Postgres and stuck on a point that I couldn't find a way to achieve. I have a simple database which are the attributes:
CREATE TABLE public.department
(
"deptId" integer NOT NULL PRIMARY KEY,
name character varying(30) COLLATE pg_catalog."default" NOT NULL,
"parentId" integer,
"numEmpl" integer NOT NULL,
CONSTRAINT "department_parentId_fkey" FOREIGN KEY ("parentId")
REFERENCES public.department ("deptId") MATCH SIMPLE
ON UPDATE NO ACTION
ON DELETE NO ACTION
)
and then I have some data in the table. Short example is
insert into department values (1, 'Headquarter', 1, 10);
insert into department values (2, 'Sales', 1, 15);
insert into department values (3, 'Logistics', 1, 25);
...
I was trying to get the total number of people who are employeed in each second level department.
I am able to get the total number of employeed people in each department but according to my search in the internet this is possible with "Hierarchical Queries". Currently, I am using
parentId=1
while querying.
Any solutions for this? Thank you.
Here is one option:
with recursive cte as (
select deptid as rootid, deptid from department where parentid = 1 and deptid <> 1
union all
select c.rootid, d.deptid
from cte c
inner join department d on d.parentid = c.deptid and d.deptid <> 1
)
select rootid, count(*) cnt from cte group by rootid
See table according to another tables ID.
Example: see what countries from country table an id = 5 from users table has visited.
I think it needs a subquery for this task.
Select * from country where (select id from users where id = 5)
It doesn't work correctly.
Edit
user table
CREATE TABLE `user` (
`id` int(6) NOT NULL,
`name` varchar(30) NOT NULL,
PRIMARY KEY (`id`)
);
INSERT INTO `user` (`id`, `name`) VALUES
('1', 'jackie'),
('2', 'maria'),
('3', 'sandra')
country table
CREATE TABLE `country` (
`name` varchar(30) NOT NULL,
`capital` varchar(30) NOT NULL,
) ;
INSERT INTO `country` (`name`, `capital`) VALUES
('Italy', 'Rome'),
('Portugal', 'Lisbon'),
('China', 'Beijing'),
('Norway', 'Oslo');
Purpose: users can mark the countries visited so the program should have the ability to show which countries a user has visited.
Hence we want a query that shows the info for each country a user with id = 5 has visited.
Example user = 5 has visited Italy and Norway.
UPDATE NEW
to add countries a user has visited:
CREATE TABLE `country_visited`(
`userId` INT(6) not null,
`country` varchar(30) not null
);
INSERT INTO `country_visited` (`userid`,`country`) VALUES
('1', 'Spain'),
('2', 'Norway'),
('3', 'Italy'),
('4', 'Spain'),
('5', 'Italy'); #if this has visited 3 countries how do you add it?
You first need a table to store which countries a user had visited. For example
CREATE TABLE countryVisited(
userId INT not null
country varchar(30) not null
)
Insert into the table:
INSERT INTO countryVisited (userId,country) VALUES
(5, 'Norway'),
(4, 'Spain'),
(5, 'Italy')
You can then join as follows:
SELECT id, name, c.country, capital
FROM users u
INNER JOIN countryVisited cv
ON u.id = cv. userId
INNER JOIN country c
ON cv.country = c.country
WHERE u.id=5
Even better, add an id field to the country table and only store that value in the countryVisited table instead of the country name.
You should have another table which stores the relation between User and Country. Something like this:
UserCountries Table
UserID CountryId
------- -------------
1 1
1 2
2 1
2 3
Then you should write a query like this:
Select * from Country where Id in
(select CountryId from UserCountries
where UserId = 5)
After edit your question I can understand the matter. Now you can use the structure for solved your problem.
Edit your user table as like as user_id, user_name, visited_country_id.
when a user choose his visited country then update user table visited_country_id using comma separator. For an Example
user_id user_name visited_country_id
5 Selim 1,3,4
Now you execute query like select* from country where country_id in (select visited_country_id from user where user_id=5)
I have two different table student and grades;
grade table has an attribute student_id which references student_id from student table.
How do I find which student has every grade that exists?
If this is not clear,
Student ID Name
1 1 John
2 2 Paul
3 3 George
4 4 Mike
5 5 Lisa
Grade Student_Id Course Grade
1 1 Math A
2 1 English B
3 1 Physics C
4 2 Math A
5 2 English A
6 2 Physics B
7 3 Economics A
8 4 Art C
9 5 Biology A
Assume there is only grade a,b,c (no d, e or fail)
I want to find only John because He has grade a,b,c while
other student like Paul(2) should not be selected because he does not have grade c. It does not matter which course he took, I just need to find if he has all the grades out there available.
Feel like I should something like exist or all function in sql but not sure.
Please help. Thank you in advance.
I would use GROUP BY and HAVING, but like this:
SELECT s.Name
FROM Student s JOIN
Grade g
ON s.ID = g.Student_Id
GROUP BY s.id, s.Name
HAVING COUNT(DISTINCT g.Grade) = (SELECT COUNT(DISTINCT g2.grade) FROM grade g2);
You say "all the grades out there", so the query should not use a constant for that.
You can use HAVING COUNT(DISTINCT Grade) = 3 to check that the student has all 3 grades:
SELECT Name
FROM Student S
JOIN Grade G ON S.ID = G.Student_Id
GROUP BY Name
HAVING COUNT(DISTINCT Grade) = 3
Guessing at S.ID vs S.Student on the join. Not sure what the difference is there.
By using exists
select * from student s
where exists ( select 1
from grades g where g.Student_Id=s.ID
group by g.Student_Id
having count(distinct Grade)=3
)
Example
with Student as
(
select 1 as id,'John' as person
union all
select 2 as id,'Paul' as person
union all
select 3 as id,'jorge'
),
Grades as
(
select 1 as Graden, 1 as Student_Id, 'Math' as Course, 'A' as Grade
union all
select 2 as Graden, 1 as Student_Id, 'English' as Course, 'B' as Grade
union all
select 3 as Graden, 1 as Student_Id, 'Physics' as Course, 'C' as Grade
union all
select 4 as Graden, 2 as Student_Id, 'Math' as Course, 'A' as Grade
union all
select 5 as Graden, 2 as Student_Id, 'English' as Course, 'A' as Grade
union all
select 6 as Graden, 2 as Student_Id, 'Physics' as Course, 'B' as Grade
)
select * from Student s
where exists ( select 1
from Grades g where g.Student_Id=s.ID
group by g.Student_Id
having count(distinct Grade)=3
)
Note having count(distinct Grade)=3 i used this as in your sample data grade type is 3
Before delving into the answer, here's a working SQL Fiddle Example so you can see this in action.
As Gordon Linoff points out in his excellent answer, you should use GroupBy and Having Count(Distinct ... ) ... as an easy way to check.
However, I'd recommend changing your design to ensure that you have tables for each concern.
Currently your Grade table holds each student's grade per course. So it's more of a StudentCourse table (i.e. it's the combination of student and course that's unique / gives you that table's natural key). You should have an actual Grade table to give you the list of available grades; e.g.
create table Grade
(
Code char(1) not null constraint PK_Grade primary key clustered
)
insert Grade (Code) values ('A'),('B'),('C')
This then allows you to ensure that your query would still work if you decided to include grades D and E, without having to amend any code. It also ensures that you only have to query a small table to get the complete list of grades, rather than a potentially huge table; so will give better performance. Finally, it will also help you maintain good data; i.e. so you don't accidentally end up with students with grade X due to a typo; i.e. since the validation/constraints exist in the database.
select Name from Student s
where s.Id in
(
select sc.StudentId
from StudentCourse sc
group by sc.StudentId
having count(distinct sc.Grade) = (select count(Code) from Grade)
)
order by s.Name
Likewise, it's sensible to create a Course table. In this case holding Ids for each course; since holding the full course name in your StudentCourse table (as we're now calling it) uses up a lot more space and again lacks validation / constraints. As such, I'd propose amending your database schema to look like this:
create table Grade
(
Code char(1) not null constraint PK_Grade primary key clustered
)
insert Grade (Code) values ('A'),('B'),('C')
create table Course
(
Id bigint not null identity(1,1) constraint PK_Course primary key clustered
, Name nvarchar(128) not null constraint UK_Course_Name unique
)
insert Course (Name) values ('Math'),('English'),('Physics'),('Economics'),('Art'),('Biology')
create table Student
(
Id bigint not null identity(1,1) constraint PK_Student primary key clustered
,Name nvarchar(128) not null constraint UK_Student_Name unique
)
set identity_insert Student on --inserting with IDs to ensure the ids of these students match data from your question
insert Student (Id, Name)
values (1, 'John')
, (2, 'Paul')
, (3, 'George')
, (4, 'Mike')
, (5, 'Lisa')
set identity_insert Student off
create table StudentCourse
(
Id bigint not null identity(1,1) constraint PK_StudentCourse primary key
, StudentId bigint not null constraint FK_StudentCourse_StudentId foreign key references Student(Id)
, CourseId bigint not null constraint FK_StudentCourse_CourseId foreign key references Course(Id)
, Grade char /* allow null in case we use this table for pre-results; otherwise make non-null */ constraint FK_StudentCourse_Grade foreign key references Grade(Code)
, Constraint UK_StudentCourse_StudentAndCourse unique clustered (StudentId, CourseId)
)
insert StudentCourse (StudentId, CourseId, Grade)
select s.Id, c.Id, x.Grade
from (values
('John', 'Math', 'A')
,('John', 'English', 'B')
,('John', 'Physics', 'C')
,('Paul', 'Math', 'A')
,('Paul', 'English', 'A')
,('Paul', 'Physics', 'B')
,('George', 'Economics','A')
,('Mike', 'Art', 'C')
,('Lisa', 'Biology', 'A')
) x(Student, Course, Grade)
inner join Student s on s.Name = x.Student
inner join Course c on c.Name = x.Course