Database - Interview Questions and Answers for 'Joins' | Search Interview Question

Database - Interview Questions and Answers for 'Joins' - 13 question(s) found - Order By Newest

Frequently asked in Cognizant ( Based on 2 feedback )

Q1. What are Inner , Outer , Left and Right Joins in SQL ?

Ans. Inner join is the intersection of two tables on the condition defined by the where clause i.e will get records from both tables matched by a column.

Outer join is the union of two tables i.e will get all records from both tables and will put null in the columns where related records are not present.

Left Outer join is the left union of two tables i.e all records from the table on the left and values from the right table for related records else null for the columns from right table.

Right Outer join is the right union of two tables i.e all records from the table on the right and values from the left table for related records else null for the columns from left table.

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Not frequently asked as it was introduced with Java 8.

Q2. What is StringJoiner ?

Core Java

Ans. StringJoiner is a util method to construct a string with desired delimiter. This has been introduced with wef from Java 8.

Sample Code

StringJoiner strJoiner = new StringJoiner(".");

strJoiner.add("Buggy").add("Bread");

System.out.println(strJoiner); // prints Buggy.Bread

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Q3. What is a self Join and give an example of a self Join ?

or

What is self Join and What is it's purpose ?

Database

Ans. When a Table Join itself , it's a Self Join. For example - we like to know the pair of department names where first dept has lesser employees than the later.

Select D1.name , D2.name from Dept D1, Dept D2 where D1.employee_count < D2.employee_count

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Q4. Difference between Inner and Outer Join ?

Database

Ans. Inner join is the intersection of two tables on a particular columns whereas Outer Join is the Union of two tables.

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Rarely asked as it was introduced with Java 8.

Q5. Which of the following has been introduced with Java 8 ? a. StringBuffer b. StringBuilder c. StringFilter d. StringJoiner

Core Java

Ans. StringJoiner

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Q6. If Table A has 100 records and Table B has 50 records , how many records will the equi join of Table generate ?

SQL

Ans. It depends on the join condition.

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Q7. If Table A has 100 records and Table B has 50 records , how many records will the left join of Table A with Table B generate ?

SQL

Ans. 100 records

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Q8. If Table A has 100 records and Table B has 50 records , how many records will the right join of Table A with Table B generate ?

SQL

Ans. 50 records

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Q9. If Table A has 0 records and Table B has 50 records , how many records will the equi join of Table generate ?

SQL

Ans. 0 records

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Q10. What is Left Outer Join ?

Database

Ans. It returns all the rows form the left table and matches the rows in both tables.

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Q11. Describe SQL Joins

Database

Ans. Oracle having following types of joins these are also called 8i joins. There are:

1. Equi (or) Inner join
2. Non Equi join
3.Self join
4.Outer join

Oracle also support the 9i (or) ANSI standard joins.There are:

1.Inner join
2.Left outer join
3.Right outer join
4.Full outer join
5.Natural join

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Q12. create an SQL query across multiple tables involving outer joins

Database

Ans. Select * from table1 t1Left outer join table2 t2 on t1.tid = t2.id

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Q13. What is the minimum number of tables required to perform a SQL join?

Database

Ans. 1 , We can do self join

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Q14. In majority of the cases, the following join will give maximum number of results ? Reference

Database

a. Inner Join

b. Outer Join

c. Left Join

d. Right Join

Ans.b. Outer Join

Q15. Which if the following is true for SQL Joins ? Reference

Database

a. Left Join and Right Join gives equal number of Results

b. Outer Join and Inner Join gives equal number of Results

c. Inner Join gives maximum number of results records

d. Inner Join gives minimum number of result records

Ans.d. Inner Join gives minimum number of result records

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