DBMS, SQL Interview Questions


SQL Queries:

  • What are outer Joins?
  • What is Index?
  • What is the difference between primary key and unique key?
  • What is the condition for UNION and what is difference between UNION and UNION ALL, which is better from performance stand point and why?
  • If there are two entities Emp and Project there is many-2 relationship, in normalized scenario, how many tables are required to capture this relationship?
  • What is difference between View, table?
  • How you will find 5 highest salary of emp?
  • Find max salary from Emp (id,age,sal)?
  • Find second max salary from Emp(id,age,sal)?
  • Any simple Example of group by clause?
  • Difference between primary & unique key?
  • Difference between HAVING and WHERE clause?
  • Query using GROUP BY and HAVING?
  • Query using grouping functions(like Max, Min)?
  • Difference between UNIQUE and PRIMARY KEY?
  • Sub query and Correlated sub query?
  • Difference between Cartesian product vs Join?

DBMS Concepts:

  • What is the primary key and can primary key contain more than 1 column?
  • What is index and is it mandatory to define index while defining the index?
  • What are the types of joins?
  • What is the difference between outter joins and inner join?
  • What is left outter, right outter and full outter join and what will be the output if 2 tables are joined using full outter join?
  • How can we indentify duplicate records in a table?
  • How can we establish many-to-many relationship between 2 tables?


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