SQL

Table of Contents

sql Interview coding/Query questions

1- How to find duplicates in a table

2- How to delete duplicates from a table

3- Difference between union and union all

4- Difference between rank,row_number and dense_rank

5- Find records in a table which are not present in another table

6- Find the second highest salary employees in each department

7- Find employees with salary more than their manager’s salary

8- Difference between inner and left join

9- update a table and swap gender values.

Normalization
- Explain the normalization process and why it’s important.
- Discuss different normal forms (1NF, 2NF, 3NF, BCNF).
Indexing:
- What are indexes, and how do they improve query performance?
- Write a query to create an index on the salary column of the employee table.

CREATE INDEX idx_salary 
ON employee(salary);

Transactions and Concurrency:
- Explain ACID properties.
- Write a query to start a transaction, update a record, and then commit the transaction.sqlCopy

START TRANSACTION; 
    UPDATE employee 
    SET salary = salary * 1.1 
    WHERE department = 'Sales'; 
COMMIT;