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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;
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NATURAL JOIN Syntax

SELECT* FROM student NATURAL JOIN teaches 17:16:44 FAILED [SELECT* - 0 rows, 0.023 secs] [Code: 102, SQL State: 42000] Falsche Syntax in der Nähe von "teaches". I really don't see the Syntax Error, what Problem could this be? Thanks in…
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Difference between natural join and simple join on common attribute in algebra

I have a confusion. Suppose there two relation with common attribite A. Now is (R natural join S)=(R join S where join condition A=A)? Natural join returns a common column A Do simple join return two columns with same name AA or 1 common column A…
simranjit singh
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SQL: Finding rows containing phrases regardless of case

Here is the database I'm using: https://drive.google.com/file/d/1ArJekOQpal0JFIr1h3NXYcFVngnCNUxg/view?usp=sharing List the deptnum and total number of academics for CS departments, in alphabetical order of deptname. CS departments are departments…
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Natural Join in Relational Algebra - Database Theory

Could I have still came up with the correct answer if I deleted the yellow part? Is it even neccesary?
user6223373
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naural join is giving Cartesian product of two relations

I have two relations, emp(id,name) and emp2(name,city,salary) with values: and relation emp2 values : As you can see, when I run natural join between them I get their Cartesian product. But why, since they have a common attribute (name)?
Manish Bharti
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SQL Natural Join Dilemma re Order, Customer & Salesman tables

I was given the following question: Write a SQL statement to make a join on the tables salesman, customer and orders in such a form that the same column of each table will appear once and only the relational rows will come. I executed the…
Varunika Gupta
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joining multiple tables in an SQL query

I'm trying to select information from multiple tables within my database which display the details of multiple books and orders. I am querying the isbn into 5 tables (author, bookauthor, book, orderline, and bookorder) of a certain book to retrieve…
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Relational Algebra Cross Join (Cross Product) and Natural Join

When do I use operators Cross Join (Cross Product) and Natural Join in a relational algebra statement?
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Natural join 3 relations which order gives better performance?

For its optimizing process, Does it join with the relation which has larger result or the one has smaller result?
RhumB
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Natural Join of two relations with more than 1 common attribute?

My actual task: Are the following two relations equivalent, why, why not?/) r5: PROJECT B (R) JOIN PROJECT B (U) r6: PROJECT B (R JOIN U) img http://s29.postimg.org/hgfgfmptx/zzz.png while R(ABC) and U (AB) I've concluded that r5 will generate a…
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Natural join opertaion returns only the first table in mysql database

i have 2 tables in my database , one is called personalfirstteaminfo and the second one is status-kids the common column between the two tables is player_id i would like to make a query that joins the two tables , and also creats an age column for…
Max Chernin
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Natural join subset decomposition

For this question , I found the answer is (c). but I can give an example to show that (c) is not correct. which is the answer? Let r be a relation instance with schema R = (A, B, C, D). We define r1 = ‘select A,B,C from r’ and r2 = ‘select A, D from…
Mehul Jain
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(MySQL) How do you get the no of unique values in a column from the resultant table of a Natural Join in a single query?

I have two Tables: Employee emp_id, emp_name, emp_dept, emp_sal 1 A A 1 2 B B 2 3 C C 3 4 D D 4 Trial emp_id, random 1 X 1 …
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Find the Cardinality of Natural Join

|X| represents number of tuples in X bold letters represent keys in the relation Consider the relations R(A, B) and S(A, C), and that R has a foreign key on A that references S. |R ✶ S| (where ' * ' represents natural join) is: The options are:…
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Types of Joins between 2 tables example - Natural Join

I have attached the question I am struggling with. So far for the question, I have worked out number of tuples for each type of join I got : R4 = 15(full join, so 10 in first table & 5 in the second) R3=?, R2 = 5, and R1 = 10. The correct answer is…
Liam
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