Interview Questions and Answers for 'Sql' | Search Interview Question

Interview Questions and Answers for 'Sql' - 49 question(s) found - Order By Rating

Q1. Write SQL query to join 2 tables ?

SQL

Ans. Select * from table1 join Select * from table2

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Q2. Sort an Employee Object based on Name or Age

Database

Ans. Use Comparable or Comparator interface

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Q3. 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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Q4. Can we load Yaml files into AWS DynamoDB ?

Amazon Web Services (AWS)

Ans. No

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Q5. 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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Q6. What is the ideal use case for DynamoDB ?

Amazon Web Services (AWS)

Ans. Fast reads
Much more reads than writes

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Q7. What is the use of sql dialect ?

Hibernate

Ans. Dialect means "the variant of a language".

Similarly in case of SQL Dialect we specify what dialect of SQL to be generated keeping in mind of underlying database.

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Q8. Given an Employee Table with Salary Column, Find 2nd and 5th highest salary in a particular department.

SQL

Ans. Select salary from (select salary from employee where department = order by salary desc limit 5) emp order by salary limit 1 AND Select salary from (select salary from employee where department = order by salary desc limit 2) emp2 order by salary limit 1

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Q9. Write SQL to get all members and the count of books they have checked out , even the ones that haven't checked out anything.

SQL

^{This question was recently asked at 'Canopy Tax'.This question is still unanswered. Can you please provide an answer.}

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Q10. Difference between Left and Inner Join ?

SQL

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Q11. What are different types of No Sql Databases ?

NoSql

Ans. graph based
column based
document based

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Q12. What are different in memory data structures that are used in No Sql Database ?

NoSql Database

^{This question is still unanswered. Can you please provide an answer.}

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Q13. 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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Q14. 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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Q15. Is there any schema in mongo DB ?

MongoDB

Ans. There is schema in mongo-db but the schema need not to be defined before creating collection.

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Q16. Write an SQL to get Employees who are also Managers

SQL

Ans. SELECT A.NAME FROM EMPLOYEE A, EMPLOYEE B WHERE A.ID = B.MANAGER_ID

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Q17. Write a SQL to display all duplicate names from Employee Table

SQL

Ans. SELECT * FROM EMPLOYEE A WHERE A.ROW_ID IN (SELECT MAX(ROW_ID) FROM EMPLOYEE b WHERE A.NAME = B.NAME )

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Q18. Write a SQL to find max salary by Dept

SQL

Ans. SELECT MAX(SALARY),DEPT FROM EMPLOYEE GROUP BY DEPT

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Q19. Write a SQL to find 2nd Max value in a Table.

Database

Ans. SELECT MIN(FIELD) FROM (SELECT TOP 2 FIELD FROM TABLE ORDER BY FIELD DESC)

or

SELECT MAX(FIELD) FROM TABLE WHERE FIELD NOT IN (SELECT MAX(FIELD) FROM TABLE)

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Q20. Which is the best NoSql Database for Performance ?

NoSql

Ans. Possible Answer - doument base - monogodb

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Q21. Which of the following databases - Cassandra / Oracle - provides more flexibility about querying the database ?

Database

Ans. Oracle as it is not modeled for a particular query or set of queries.

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Q22. How different is the Search algorithm when we query Cassandra Tables and When we query Oracle Tables ?

Cassandra

Ans. Relational Database uses linear search if we don't query using indices. Performance for linear search is O(n). If indices have been used , relational database uses binary search. Performance for binary search is O(Log n).

Casandra uses hash search. Performance for Hash Search is O(1).

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Q23. Write a SQL to remove records with a duplicate field in a Table ?

Database

^{This question was recently asked at 'Sofi'.This question is still unanswered. Can you please provide an answer.}

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Q24. 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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Q25. 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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Q26. 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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Q27. 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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Q28. What do you make out of this error

org.hibernate.exception.ConstraintViolationException: could not insert: [<Entity>]
Caused by: java.sql.SQLIntegrityConstraintViolationException: ORA-00001: unique constraint (<Constraint Name>) violated

and how would you go about debugging it ?

Database

Ans. Application is unable to insert a record as it violates a unique constraint.

The exception states the constraint and Table can be located by the Entity mapping. So I will go to the DB and will first check to which all columns the unique constraint applies. And then I will go and check the code and logs to see how come the duplicate column values were attempted to be inserted when they were not supposed to be.

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Frequently asked in Cognizant ( Based on 2 feedback )

Q29. What are Inner , Outer , Left and Right Joins in SQL ?

Database

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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Q30. With a Table employee having columns Id,Name,ManagerEmployeeId, Write a SQL to find the Manager with maximum number of employees ?

Database

Ans. Select Name from EMPLOYEE where ID in (Select ManagerEmployeeId from EMPLOYEE
Group By ManagerEmployeeId
order by count(Id)
LIMIT 1)

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