Preparing for an SQL interview? Get ready with our comprehensive list of SQL interview questions, including common questions for SQL interviews, important SQL interview topics.
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Are you preparing for an SQL interview? Great. Databases are significant, but a good command of SQL is essential. We have compiled everything for you: the most exhaustive guide with SQL interview questions, common SQL interview questions, critical SQL interview topics. This will make sure you are prepared and confident in any SQL-related job interview.
In this article, we will cover Top 50+ SQL Interview Questions with answers asked in SQL interviews at MAANG and other high-paying companies. this article will help you better prepare for the SQL interview and know what to expect from your interviewer/interviewee.
What is SQL and what are its uses?
SQL, which stands for Structured Query Language, manages and manipulates relational databases. It is utilized to read, update, create, and delete data in a database.
What is a primary key in SQL?
A primary key is a unique identifier for a database record, which ensures that each record in the database can be distinguished without any ambiguity. It provides that no data in the table gets duplicated.
What is a foreign key?
A foreign key is a field in a table whose value depends on another field in a different table. It establishes a relationship between two tables while maintaining the referential integrity.
Explain the concept of normalization and its types.
Normalization refers to structuring data so that redundancy can be minimized. Such a process reduces the risk of data inconsistency. The different types are as follows:
- First Normal Form (1NF) — Ensures that every column has atomic values and every row is unique.
- Second Normal Form (2NF) — Ensures that all attributes are fully functional and dependent on a key that is not a child key.
- Third Normal Form (3NF) — Ensures that no transitive dependencies exist, meaning non-key attributes depend only on the key.
What are joins in SQL and their types?
An INNER JOIN combines rows from two or more tables based on a related column. Common types of joins include:
- INNER JOIN: Combines records with matching values in both tables.
- LEFT JOIN or LEFT OUTER JOIN: Combines all records from the left table and only the matched records from the right table.
- RIGHT JOIN or RIGHT OUTER JOIN: Combines all records from the right table and only the matched records from the left table.
- FULL JOIN (or FULL OUTER JOIN): Return all records when a match is in either table.
What is a subquery in SQL?
A subquery is a query whose some part is among another inquiry. It is more complex and efficient in terms of getting data through it. The reason one would like to use subqueries can be that they can appear alongside SELECT, INSERT, UPDATE, or DELETE queries.
Explain the meaning of SQL dialects. Give some examples.
SQL dialects represent the various forms or versions of SQL, which is available freely or at a fee. These dialects are all different in minor aspects of feature implementations as additional features have been added to them. For instance, they include Microsoft SQL Server, PostgreSQL, MySQL, SQLite, T-SQL, Oracle, and MongoDB.
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