A join in which the joining condition is based on equality between values in the common columns is called a(n):

Question

BlackTom AI · Accepted Answer

An equi-join uses the equality operator (=) on the common columns to pair rows from two relations, so the correct answer is equi-join.

1) Relevant knowledge points and concepts
- A join combines rows from two tables based on a condition.  
- A theta-join is a join that uses any comparison operator (>, <, =, ≠, etc.).  
- An equi-join is the special case of a theta-join where the comparison operator is equality ("=").  
- A natural join is a further special case of an equi-join that automatically matches all columns with the same names and removes duplicate columns in the output.  
- Implementation-wise, equi-joins are commonly executed with nested loops, sort-merge, or hash-join algorithms using the equality condition.

2) Step-by-step reasoning with an example
- Suppose Table R(A,B) contains rows: (1, 'x'), (2, 'y').  
- Suppose Table S(B,C) contains rows: (1, 'a'), (3, 'b').  
- The equi-join R.A = S.B would evaluate equality for every pair:
  - Compare R(1,'x') with S(1,'a'): 1 = 1 → match → output (1,'x',1,'a').  
  - Compare R(1,'x') with S(3,'b'): 1 = 3 → no match.  
  - Compare R(2,'y') with S(1,'a'): 2 = 1 → no match.  
  - Compare R(2,'y') with S(3,'b'): 2 = 3 → no match.  
- Result set contains only the matching row(s) where equality holds.

3) Why the correct answer is correct
- The question specifies "joining condition is based on equality between values in the common columns" which exactly defines an equi-join: the join predicate is equality on columns.

4) Why other options are incorrect
- "equality-join" is not the standard term used in relational theory and is uncommon; the standard term is equi-join.  
- "unilateral join" is not a standard relational algebra join type.  
- "match-join" is also not a standard term in relational algebra (it is ambiguous and not used as the canonical name).

Conclusion: The correct and standard term for a join whose condition is equality on common columns is "equi-join," which matches the provided answer.

A join in which the joining condition is based on equality between values in the common columns is called a(n):Single choice

Similar Questions

SELECT the SQL statement that will list the first name, last name, city, and country where they work.

Select the SQL statement that will list the first_name, last_name and the name of the department they work for. Be sure to select the syntactically correct statement.

The following code is an example of a(n): SELECT Customer_T.CustomerID, Order_T.CustomerID, CustomerName, OrderID FROM Customer_T, Order_T WHERE Customer_T.CustomerID = Order_T. CustomerID;

The most commonly used form of join operation is the:

Which join type could be used to answer the following question? Show all information for products in the Electronics category, whether or not they have ever been ordered, and also show any related order details they may have. Choose all that apply.

要连接两个或多个表，应该使用哪条 SQL 语句？

Below are the Movies and Sales table of a relational database: Dexter has created the following SQL query: SELECT tblMovies.Title, tblMovies.Genre, tblSales.CopiesFROM tblMovies, tblSalesWHERE tblMovies.MovieID = tblSales.MovieID How many records will be returned by the query?

More Practical Tools for Students Powered by AI Study Helper

Homework AI Solver

Stylized AI Paper Writer

Plagiarism Checker Assistant

Citation AI Academic Writing Tool

In-Class Translation Assistant

AI Note Generator

AI Quiz Answers

Past Exam Questions from University Test Bank

Smart Practice Assistant

Adaptive Practice

Making Your Study Simpler