The 10 SQL Job Interview Questions You Should Know How to Answer

The 10 SQL Job Interview Questions You Should Know How to Answer

SQL, used for relational database management systems, is one of the most popular coding languages. Now, with the breakneck growth of data, it is no secret companies worldwide are looking to hire SQL specialists.

Check out the SQL job interview cheat sheet: Here are our top tips for answering the 10 most common SQL job interview questions.

What is SQL?

SQL is structured query language. It is a programming language designed explicitly for databases. However, some may argue it is not a “true” programming language because it was not created with conditional statements, for loops or other procedural-language procedures.

SQL executes commands for querying, creating, inserting, updating and deleting data in a database.

What is a database? What is a DBMS?

A database is data stored on a computer and organized to make it easy to access and manipulate. The software tool that allows the user to interact with the data stored in the database is called a database management system or DBMS.

There are two types of database management systems: relational and non-relational database management systems. SQL works with relational database management systems.

What is the difference between DDL, DML, DCL and TCL?

DDL, DML, DCL and TCL are SQL commands.

  • Data Definition Language (DDL) allows you to CREATE, DROP, ALTER, and TRUNCATE data structures.
  • Data Manipulation Language (DML) involves commands for manipulating information. It allows you to SELECT, INSERT, UPDATE and DELETE data. DML is often used in data science or business intelligence.
  • Data Control Language (DCL) consists of commands typically used by database administrators. DCL allows the programmer to GRANT and REVOKE rights delineating how much control you can have over the information in the database.
  • Transaction Control Language (TCL) also contains commands applied by database administrators. TCL ensures the database’s transactions can minimize the danger of data loss.

What are foreign key constraints?

Foreign key constraints are rules or limits that will ensure that the values in the child and parent tables match. Typically, foreign key constraints will maintain the referential integrity within the database.

What is “inner join,” and how is it used?

A SQL join is a tool that allows you to construct a relationship between objects in your database. Consequently, a join shows a result set containing fields derived from two or more tables.

For example, assume you have data about customer IDs and a customer’s sales in one table, and in another, you have data about customer IDs and private information.

An inner join allows you to obtain an output containing information from both tables. For instance, you might only want customer IDs found in the two tables that match.

What is a “left join,” and how is it used?

Unlike an inner join, a left join will ensure that we extract information from both tables.

Using the customer IDs tables example, a left join will show null values for IDs that are only found in the left table in the place of the columns from the right table.

What is the difference between MySQL and PostgreSQL?

MySQL and PostgreSQL are two versions of SQL or structured query language.

PostgreSQL supports outer joins while MySQL doesn’t. With MySQL, you need to use UNION or UNION ALL to emulate an outer join in PostgreSQL.

What is the difference between PL/SQL and SQL?

PL/SQL is a complete procedural programming language, and its score of application is different from SQL. PL/SQL is not a version of SQL.

What is a SQL view?

A view is a virtual table whose contents are obtained from an existing table or tables, called base tables. The retrieval happens through an SQL statement incorporated into the view.

You can think of a view object as a view into the base table. The view itself does not contain any real data; the data is electronically stored in the base table. The view simply shows the data contained in the base table.

This article was written by 365 Data Science for HackerNoon and was lightly edited and published with permission.