Stack Overflow
Stack Overflow

Questions tagged [natural-join]

A natural join is a relational operation that joins on the like-named attributes between tables

Natural join (⋈) is a binary operator that is written as (R⋈S) where R and S are relations. The result of the operation is the set of all combinations of tuples in R and S that have equal values on their common attribute names. The resulting relation has a heading consisting of the set-union of the attributes from R and S, i.e. there are no duplicate attribute names in the result.

If the joined relations have no attribute names in common then R⋈S is equivalent to R×S (Cartesian product).

The natural join of any relation, R, to itself is R (R⋈R = R).

The ISO Standard SQL syntax for natural join (R⋈S) is:

SELECT * FROM R NATURAL JOIN S;
124 questions
245
votes
12 answers

Difference between natural join and inner join

What is the difference between a natural join and an inner join?
smith
  • 5,341
  • 8
  • 31
  • 38
26
votes
2 answers

Join tables on columns of composite foreign / primary key in a query

CREATE TABLE subscription ( magazine_id bigint, user_id bigint, PRIMARY KEY (magazine_id, user_id) ); CREATE TABLE delivery ( magazine_id bigint, user_id bigint, FOREIGN KEY (subscription) REFERENCES subscription…
samol
  • 18,950
  • 32
  • 88
  • 127
22
votes
3 answers

Natural join if no common attributes

What will natural join return in relational algebra if tables don't have attributes with same names? Will it be null or the same as cross join (cross product) (Cartesian product)?
Hate
  • 1,185
  • 3
  • 12
  • 24
12
votes
3 answers

Oracle USING clause best practice

Disclaimer: I'm a developer and not a DBA. I've been a huge fan of the USING clause in Oracle since I accidentally stumbled upon it and have used it in place of the old-fashioned ON clause to join fact tables with dimension tables ever since. To me,…
RAY
  • 6,810
  • 6
  • 40
  • 67
10
votes
6 answers

Is NATURAL (JOIN) considered harmful in production environment?

I am reading about NATURAL shorthand form for SQL joins and I see some traps: it just takes automatically all same named column-pairs (use USING to specify explicit column list) if some new column is added, then join output can be "unexpectedly"…
Grzegorz Szpetkowski
  • 36,988
  • 6
  • 90
  • 137
10
votes
5 answers

Natural join with more than one common attribute in two tables

I can understand how natural join works when the two tables have only one common attribute. What if they have two ones? Table 1 have 3 attributes: A, B, C Table 2 has 3 attribute: A, B, D First two rows in table 1: 1 2 3 4 5 6 First two rows in…
Hiep
  • 109
  • 1
  • 2
  • 6
6
votes
1 answer

mysql natural join not working

I have two tables in mysql server. I use these tables for studing JOIN multiple tables but something appears to be incorrect: mysql> select * from category; +-------------+-----------+ | category_id | name | +-------------+-----------+ | …
Влад Христенко
  • 121
  • 2
  • 4
6
votes
4 answers

maximum and minimum number of tuples in natural join

I came across a question that states Consider the following relation schema pertaining to a students database: Student (rollno, name, address) Enroll (rollno, courseno, coursename) where the primary keys are shown underlined. The number of…
user1765876
5
votes
3 answers

Difference between cross product (cross join, Cartesian product) and natural join

While writing in SQL, how would I know if I should use cross product (cross join, Cartesian product) or natural join?
AamKhayega
  • 89
  • 1
  • 1
  • 3
5
votes
1 answer

SQLite natural join broken?

I am just getting to know NATURAL JOIN and SQLite is not behaning as I expect. SELECT * FROM r1 NATURAL JOIN (r2 NATURAL JOIN r3); and SELECT * FROM (r1 NATURAL JOIN r2) NATURAL JOIN r3; produce the same (correct) results. However if I omit the…
Panayiotis Karabassis
  • 2,278
  • 3
  • 25
  • 40
4
votes
4 answers

Oracle Natural Joins and Count(1)

Does anyone know why in Oracle 11g when you do a Count(1) with more than one natural join it does a cartesian join and throws the count way off? Such as SELECT Count(1) FROM record NATURAL join address NATURAL join person WHERE status=1 AND code =…
Aaron Smith
  • 3,332
  • 4
  • 29
  • 25
3
votes
4 answers

Lossless Join Property

What is meant by the lossless join property in a relation schema? Is it the ability to maintain the semantics of information/data during the decomposition of relations whilst normalising?
user559142
  • 12,279
  • 49
  • 116
  • 179
3
votes
1 answer

Venn Diagram for Natural Join

I've been trying to understand the concept of sql joins fully, venn diagrams have helped me a lot to do that. I've found them for all kind of joins but not for natural joins. How would a venn diagram for a natural join look like?
Irina Crabbs
  • 49
  • 5
3
votes
2 answers

What is the difference between Join and Natural Join?

I'm learning Oracle SQL and now I'm stuck on Joins chapter. I can't understand the difference between Join and Natural Join SELECT employee_id, job_id, department_id, e.last_name, e.hire_date, j.end_date FROM …
user6611026
3
votes
2 answers

can't get natural join to work

I'm using postgresql, though I confirmed this in sqlfiddle.com too. My tables and elements are: create table Publisher(pID int PRIMARY KEY, name varchar(255), address varchar(255)); create table Book(ISBN int PRIMARY KEY, name varchar(255), genre…
TugRulz
  • 65
  • 7
1
2 3
…
8 9