Question 1:What is SQL and what does it stand for?
Answer: SQL stands for Structured Query Language which is used for managing and manipulating relational databases.
Question 2: What is the difference between SQL and MySQL?
Answer: SQL is a database language that is used for querying and managing databases. MySQL is a relational database management system (RDBMS) that uses SQL as its query language.
Question 3:What is SQL injection, and how can it be prevented?
Answer: SQL injection is a type of security vulnerability of a database where malicious SQL code is inserted into an input field, allowing attackers to manipulate the database. you can prevent this by using parameterized queries or prepared statements, escaping user inputs, and implementing proper input validation.
Question 4:What do you understand by “Index” in a database?
Answer: An index is a database structure like indexing in a book that improves the speed of data retrieval operations on a table by allowing the database to quickly locate the rows that match a certain value in the indexed column.
Question 5: What is normalization? Why is it important?
Answer: The process of organizing a database to reduce data redundancy and improve data integrity is called Normalization. This process involves breaking down a database into smaller, related tables and establishing relationships between them. Normalization is important because it prevents data anomalies and inconsistencies.
Question 6: What is the basic structure of an SQL query?
Answer: An SQL query consists of a SELECT clause (specifying columns to retrieve), a FROM clause (specifying tables), and optional clauses like WHERE (filtering), GROUP BY (grouping), HAVING (filtering after grouping), and ORDER BY (sorting).
Question 7: What is a primary key? Why is it important?
Answer: A primary key is a unique key that is used to identify a record in a table. It ensures data uniqueness and works as a reference point for establishing relationships between tables.
Question 8: What is a foreign key?
Answer: A foreign key is a field in a table that establishes a connection between that table and the primary key of another table. It enforces referential integrity and maintains relationships between tables.
Question 9: What is the purpose of the SELECT statement in SQL?
Answer: The SELECT statement retrieves data from one or more tables based on specified criteria. It is used to query the database and retrieve specific information.
Question 10: What is the difference between INNER JOIN and OUTER JOIN?
Answer: An INNER JOIN returns only the matching records from both tables, while an OUTER JOIN (LEFT, RIGHT, FULL) returns all records from one table and the matching records from the other.
Question 11: what is the difference between UNION and UNION ALL?
Answer: UNION combines the results of two or more SELECT queries and removes duplicate records, while UNION ALL combines results without removing duplicates
Question 12: What is normalization? Why is it important in database design?
Answer: Normalization is the process of organizing a database to minimize data redundancy and improve data integrity. It helps eliminate anomalies and ensures efficient storage.
Question 13: What is denormalization, and when you should use it?
Answer: The denormalization process intentionally introduces redundancy into a database to improve query performance. It’s used when read operations are more frequent and performance is a priority over data modification efficiency.
Question 14: How would you prevent SQL injection attacks in your queries?
Answer: Use parameterized queries or prepared statements, validate user inputs, and sanitize inputs by escaping special characters.
Question 15: What is the purpose of the GROUP BY clause? Explain with an example.
Answer: The GROUP BY clause is used to group rows that have the same values in specified columns. Example: “SELECT Department, AVG(Salary) FROM Employees GROUP BY Department;”
Question 16: What is SQL testing?
Answer: SQL testing is the procedure of validating frontend data with the backend system by running SQL queries and fetching data from the database.
Question 17:Why is SQL testing important?
Answer: SQL testing ensures that database interactions with the front end are accurate, efficient, and secure. It helps identify errors (if front-end input data is not matching with backend query output) and performance bottlenecks (if DB is taking too long in running the query) in SQL code and databases.
Question 18: What are some common types of SQL testing?
Answer: Common types of SQL testing are involved at the below level:
Unit Testing, Integration Testing, Functional Testing, Performance Testing, Security Testing, and Regression Testing.
Question 19: Explain the difference between “Unit Testing” and “Integration Testing” in SQL.
Answer: Unit Testing focuses on testing one component or module at a time in isolation, typically individual SQL queries, stored procedures, or functions. On the contrary side Integration Testing involves testing interactions between various components, ensuring they work together as expected, like if we are entering data in any one component and another component is processing this data and giving some result then the output of the second component should be correctly processed as per logic provided to process the data and data entered under the first component.
Question 20:How would you test a complex SQL query?
Answer: It’s recommended to write test cases with different input scenarios to cover various conditions and edge cases, also verify the expected results against the actual results from the query execution.
Question 21: What is regression testing in the context of SQL?
Answer: Regression testing in the context of SQL means re-running previously executed tests to ensure that new changes or additions to the SQL codebase have not introduced any new errors or regressions, which means the query result should be the same as before the change.
Question 22: How can you test the performance of a SQL query?
Answer: Performance testing of a SQL query means measuring query execution time and resource usage. You can use tools like EXPLAIN to analyze the query plan, also tools like Profilers and Query Performance Tuning to identify and address performance bottlenecks.
Question 23: How would you handle testing a database migration or schema change?
Answer: Follow the below steps to test database migration or schema:
Create a comprehensive test plan that includes running the same queries before-and-after change to verify data consistency.
Check indexes and constraints are properly maintained.
Perform regression testing to ensure that existing functionality is not impacted.
Question 24:What is ACID property in the context of databases?
Answer: ACID is the abbreviation of Atomicity, Consistency, Isolation, and Durability. These properties ensure that database transactions are reliable and maintain data integrity even in the face of failures.
Question 25: What do you understand by “ETL” in SQL?
Answer: ETL, an acronym for Extract, Transform, and Load, is a fundamental procedure within the realm of Data Warehousing. This procedure entails the extraction of data from diverse source systems, its subsequent transformation within a designated staging area, and ultimately, its loading into the Data Warehouse system. ETL serves as a unified tool combining three critical database functions: extracting data from one database and seamlessly transferring it to another.
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