Sql Queries Interview Questions For Testers
Mastering SQL Queries: Essential Interview Questions for Testers
Sql Queries Interview Questions For Testers
In SQL queries interview questions for testers, candidates are typically assessed on their understanding and ability to write SQL queries to retrieve data, filter results, perform joins, aggregate data, and spot errors in queries. Testers may also be asked to demonstrate their knowledge of common SQL functions, operators, and clauses, as well as their capability to write efficient and optimized queries. Additionally, testers may need to showcase their skills in using SQL to validate data integrity, verify data accuracy, and ensure the reliability of database operations. Overall, SQL queries interview questions for testers aim to evaluate their proficiency in utilizing SQL for accurate testing and analysis of data.
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1 - What is SQL injection and how can it be prevented?
SQL injection is a type of attack where malicious SQL queries are inserted into input fields of a web application, allowing attackers to access or manipulate the database. To prevent SQL injection, testers can use parameterized queries, input validation, and escape characters to sanitize user inputs.
2) Explain the difference between primary key and unique key constraints in SQL.
A primary key is a column or a group of columns that uniquely identifies each row in a table, and it cannot contain NULL values. A unique key, on the other hand, ensures that all values in the column or group of columns are unique, but it can allow NULL values.
3) How can you retrieve data from multiple tables in a single SQL query?
Testers can use joins to retrieve data from multiple tables in a single SQL query. Common types of joins include inner join, left join, right join, and full outer join, each serving a different purpose based on the relationship between the tables.
4) What is the difference between TRUNCATE and DELETE in SQL?
TRUNCATE is a DDL command that removes all records from a table, resetting the auto increment value, and is faster and does not log individual row deletions. DELETE is a DML command that removes specific rows based on the condition provided, and it logs individual row deletions, making it slower than TRUNCATE.
5) Explain the ACID properties of a transaction in SQL.
ACID stands for Atomicity, Consistency, Isolation, and Durability the four properties that ensure the reliability of transactions in a database system. Atomicity guarantees that a transaction is either fully completed or not completed at all, Consistency ensures that the database remains in a valid state before and after the transaction, Isolation prevents concurrent transactions from interfering with each other, and Durability guarantees that once a transaction is committed, it will persist even in the event of failures.
6) How can you optimize SQL queries for better performance?
Testers can optimize SQL queries by avoiding the use of wildcard characters at the beginning of a query, indexing appropriate columns, minimizing the use of subqueries, avoiding using SELECT *, and ensuring that queries are written efficiently by using appropriate functions and operators.
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