I want to join two tables where Person table fields(having Street S1) will be merged into Student table, but adding new field (STUDENT/NONSTUDENT).
Student table has 1milyon rows, Result person table has max 100 rows.
What is the best sql for performance to merge them all?
student table (name, age)
A-12
B-23
C-24
person table (name, street, live)
A-S1-L
B-S2-NL
D-S1-L
At the end I want such result
A-12-Student
D-NULL-NOTSTUDENT
This should work:
select p.name,
s.age,
case when s.name is null then 'NotStudent'
else 'Student' end as IsStudent
from person p
left join student s on p.name = s.name
where p.Street = 's1'
Related
I want to pull a person and their supervisor names from a table. The persons table has the supervisor_id and the person_id. The names table has name_id and a Full Name field. If I join Person ON either supervisor_id or person_id, how do I get the other to display as well?
You need to join twice, one for each relationship you have:
SELECT
-- Persons' columns
P.*,
-- Superviser name columns
SN.*,
-- Person name columns
PN.*
FROM
persons AS P
LEFT JOIN names AS SN ON P.supervisor_id = SN.name_id
LEFT JOIN names AS PN ON P.person_id = PN.name_id
Or you can join with an OR clause, but you won't be able to know which record did you join with unless you check with a CASE.
SELECT
-- Persons' columns
P.*,
-- name columns
N.*,
IsSupervisor = CASE WHEN P.supervisor_id = N.name_id THEN 'Yes' ELSE 'No' END
FROM
persons AS P
LEFT JOIN names AS N ON
P.supervisor_id = N.name_id OR
P.person_id = N.name_id
This last approach will display 2 rows as it will match either one or the other on different occasions, not both with the same persons row (as the first example).
A (self)join is what you need:
select p.*, supervisor=ps.name
from Person p join person ps on p.supervisor_id=ps.id
I'm doing an exercise on ORACLE SQL.
Currently I got 3 tables.
Student values = "student_id ,name"
Subjects values = "subject_id, name"
Scores values = "score, student_id, subject_id"
I'm trying to retrieve the following information from my database.
Name of student, Name and id of the subject and finally the score that has the student_id "34560".
SELECT scores.score,
scores.subject_id,
student.name,
subject.subject_id,
subject.name
FROM scores
INNER JOIN students
ON scores.student_id = '34560'
INNER JOIN subject
ON /* and here's where i'm lost*/
Is there a way to put all together from the first part of the query where I call the list of students with student_id = "34560" and then query that list to see if it matches with the subject_id?
Use in operator for list of student id
SELECT sc.score, sc.subject_id,
st.name, sb.subject_id, sb.name
FROM scores sc
INNER JOIN students st
ON sc.student_id = st.student_id
INNER JOIN subject sb
ON sc.subject_id=sb.subject_id
where sc.student_id in ('34560','add_anotherstudentid','add_anotherstudentid') //you can add multiple student id
I have three tables in my Oracle db:
Peoples:
IdPerson PK
Name
Surname
Earnings:
IdEarning PK
IdPerson
EarningValue
Awards:
IdAward PK
IdPerson FK
AwardDescription
So one person can have many earnings, one earning or can have no any earnings. Also one person can have many awards, one award, or no any award.
I have to select Surname and AwardDescription but only for people who have any earnings, because it is possible to have some award but, also don't have any earning!
My problem is to make a correct group by statement. I use query posted below and I am selecting surname of person with a description of award, but it is duplicating for each row in Earnings for this person.
SELECT AwardDescription, Surname
FROM Awards
INNER JOIN People ON People.IdPerson= Awards.IdPerson
INNER JOIN Earnings ON Earnings .IdPerson= People.IdPerson;
How to group it and avoid duplicating rows for each earning of person?
One person can be in many rows, but with different awards.
You could add DISTINCT to your query:
SELECT DISTINCT AwardDescription, Surname
FROM Awards
INNER JOIN People ON People.IdPerson= Awards.IdPerson
INNER JOIN Earnings ON Earnings .IdPerson= People.IdPerson;
Or another option is to use EXISTS:
SELECT AwardDescription, Surname
FROM Awards
INNER JOIN People P ON P.IdPerson= Awards.IdPerson
WHERE EXISTS (
SELECT 1
FROM Earnings E
WHERE P.IdPerson = E.IdPerson);
Do a left outer join among the tables like
SELECT p.Surname, a.AwardDescription, e.EarningValue
FROM People p
LEFT JOIN Awards a ON p.IdPerson= a.IdPerson
LEFT JOIN Earnings e ON e.IdPerson= p.IdPerson
WHERE a.AwardDescription IS NOT NULL
OR e.EarningValue IS NOT NULL;
I have 3 table, named as
students (id, name)
subjects (id, name, is_published)
student_subjects (id, student_id, subject_id)
The subjects taken by a student goes in student_subjects. But there are cases where student_subjects contains NULL subject_id for a student
Here's the data for Students table
1;"John"
2;"Ahmeah"
3;"Dina"
4;"Leo"
5;"Lenon"
Subjects Table
1;"Computer Sci";1
2;"Physics";1
3;"Bio";1
4;"Maths";0
Student_subjects
1;1;1
2;1;2
3;1;4
4;2;1
5;2;3
6;2;4
7;3;2
8;4;1
9;5;NULL
Currently to fetch all the students with their subjects and also display the name of the student who has no subject attached to him, I am using the query as follows
SELECT
students.*,
inners.name
FROM
students
LEFT JOIN ( SELECT
student_id,
subjects.name
FROM
student_subjects
JOIN subjects ON ( student_subjects.subject_id = subjects.id AND subjects.is_published = 1)
) AS inners ON (inners.student_id = students.id )
Is there a better way to do the same http://sqlfiddle.com/#!12/9cf93/12
SELECT s.*, su.name AS SubjName
FROM students AS s
LEFT JOIN student_subjects AS ss ON ss.student_id = s.id
LEFT JOIN subjects AS su ON su.id = ss.subject_id
Does the same thing as the one you listed. Is that what you are after?
In a relational database I have three tables. Using SQL Server.
person(id, type)
student(id, person_id, type, student specific fields)
teacher(id, person_id, type, teacher specific fields)
Student and teacher are both people, therefore a student will have a record in both the person and student tables, as will the teacher. Student and teacher have foreign keys to person. Student and teacher have different field definitions therefore a union will NOT work.
Now I have the person's id and depending on whether the person is a student or teacher I would like to select * from the relevant table (not person).
For example, if the person is a student I would like my query to select the student table.
I can think of a few inefficient methods but I am looking for the optimum one.
I would suggest a UNION
SELECT student.*
FROM student
WHERE person_id= #id
UNION
SELECT teacher.*
FROM teacher
WHERE person_id= #id
if exists(select person_id from student where person_id = #id)
select * from student where person_id = #id
else
if exists(select person_id from teacher where person_id = #id)
select * from teacher where person_id = #id
If your RDBMS is SQLServer, then I would abstract a view along the lines of podiluska's union, mapping out specific fields in Student and Teacher to common names, and padding with NULLs where no mapping is possible
And assuming that Students and Teachers inherit from person (i.e. both are 0..1 to 1 with Person), then they can share the same primary key, i.e. no need for new surrogates keys on Teacher and Student.
I've assumed that person.type determines whether the person is a Student(S) or Teacher(T).
CREATE VIEW SubClassesOfPerson AS
SELECT p.id as PersonId,
p.name as PersonName,
p.OtherBaseFieldsHere,
s.SomeStudentSpecificField AS MappedField1,
s.SomeStudentSpecificFieldX AS MappedFieldX,
s.SomeStudentSpecificField as MappedFieldForStudentOnly,
NULL as MappedFieldForTeacherOnly -- Pad this because it can't be mapped
FROM person p
INNER JOIN student s
on s.person_id = p.id AND p.type = 'S'
UNION
SELECT p.id as PersonId,
p.name as PersonName,
p.OtherBaseFieldsHere,
t.SomeTeacherSpecificField AS MappedField1,
t.SomeTeacherSpecificFieldX AS MappedFieldX,
NULL as MappedFieldForStudentOnly, -- Pad this because it can't be mapped
t.SomeTeacherSpecificField as MappedFieldForTeacherOnly
FROM person p
INNER JOIN teacher t
on t.person_id = p.id AND p.type = 'T'