SQL Interview Questions Data Science and Data Engineer Interview

 

SQL Interview Questions 

Data Science and Data Engineer Interview

• What is primary key?

• What is a unique key?

• What is a foreign key?

• What is normalization?

• What is denormalization?

• Explain the different types of normalization.

• What are views in SQL?

• What is join? Explain the different types.  (for join algorithm click here)

• What are the different types of indexes?

• What is a cursor in SQL?

• What is a subquery?

• What is a trigger?

• Differentiate between the DELETE and TRUNCATE commands.

• What are constraints?   

• What is auto increment?

• What is a data warehouse?

• What is the difference between DROP and TRUNCATE statements?

• What are aggregate and scalar functions?

• What is alias in SQL?

• What are Window Functions?

• What is the difference between OLTP and OLAP?

• How can we change a table name in SQL?

• What are nested queries?

• What is the difference between CHAR and VARCHAR2 data types in SQL server?

• What is difference between SQL and PL/SQL?

• What is the difference between SQL and MySQL?

• What is cross join?

• What are user defined functions?

• What is a CLAUSE?

• What is recursive stored procedure?

• Explain UNION, MINUS and INTERACT commands?

• Which operator is used in query for pattern matching?

• How can we select unique records from a Table?

• What is the main difference in the BETWEEN and IN condition operators?

• Is semicolon used after sql? Justify why or why not.

• What is candidate key?

• What is the difference between JOIN and UNION?

• What is the difference between order and group by?

• Write an SQL query to fetch employee names having a salary

• greater than or equal to 20000 and less than or equal to 10000.

• Name three functions that specify current date and time.

• Which function returns the difference between two periods?

• What would the format of the output be?

• How can we fetch common records from two tables?

• How can we fetch alternate records from a table?

• How can we select unique records from a table?

• What is the command used to fetch the first 5 characters of the string?

• How to use LIKE in SQL?

• How can we copy a table in SQL?

• If we drop a table, does it also drop related objects?

• Can you join a table by itself?

• Explain Equi join with an example.

• Explain non-Equi join with an example.

• How can we store videos inside SQL server table?

• Write an SQL query to show the second highest salary from a table.

• How would you select all the users whose phone number is NULL?

• Write an SQL query to fetch three max salaries from a table.

•  Write an SQL query to create a new table with data and structure copied from another table.

• What are the differences between the HAVING clause, and the WHERE clause?

• What does a BCP command do?

• Can a view be active if the base table is dropped?

• What is CTE?

• Does view contain data?

• Define a temp table.

• What is the difference between the RANK() and DENSE_RANK() function?

• What is referential integrity?

• What are nested triggers?

• Write a query to fetch 50% records from an Employee table.

• Write a query to fetch the top N records.