Multiple choice technology databases

What is true about joining tables through an equijoin

  1. You can join a maximum of two tables through an equijoin

  2. You can join a maximum of two columns through an equijoin

  3. You specify an equijoin condition in the SELECT or FROM clauses of a SELECT statement

  4. To join two tables through an equijoin, the columns in the join condition must be primary key and foreign key columns.

  5. You can join n tables (all having single column primary keys) in a SQL statement by specifying a minimum of n-1 join conditions.
Reveal answer Fill a bubble to check yourself
E Correct answer
Explanation

To understand the concept of equijoin, the user should know the basics of SQL and joins. An equijoin is a type of join that combines columns from two or more tables based on their equality.

Let's go through each option and explain whether it is true or false:

A. You can join a maximum of two tables through an equijoin

  • This statement is false. You can join more than two tables through an equijoin.

B. You can join a maximum of two columns through an equijoin

  • This statement is false. You can join more than two columns through an equijoin.

C. You specify an equijoin condition in the SELECT or FROM clauses of a SELECT statement

  • This statement is false. You specify an equijoin condition in the WHERE clause of a SELECT statement.

D. To join two tables through an equijoin, the columns in the join condition must be primary key and foreign key columns.

  • This statement is false. The columns in the join condition need not be primary key and foreign key columns; they can be any columns that have the same data type and contain the same values.

E. You can join n tables (all having single column primary keys) in a SQL statement by specifying a minimum of n-1 join conditions.

  • This statement is true. If you want to join n tables, you need to specify a minimum of n-1 join conditions.

The Answer is: E

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