How does the use of subqueries impact the performance of SQL queries, and how can it be optimized?
- Subqueries can slow down SQL queries significantly. They execute for each row in the outer query result and may lead to performance bottlenecks. Optimization techniques include using JOINs, EXISTS, or rewriting queries as JOINs, ensuring indexes on relevant columns, and limiting the result set size.
- Subqueries have no impact on SQL query performance.
- Subqueries always improve SQL query performance.
- Subqueries should be avoided, but if used, no optimization is possible.
Subqueries can impact SQL query performance negatively if not used carefully. They can lead to increased query execution times, and optimizing them involves using appropriate techniques to minimize their impact.
You have been assigned to optimize the CRUD operations of a microservices-based application where each microservice handles its own database. How would you ensure the consistency and integrity of data across different microservices while performing Create and Update operations?
- Implement a distributed transaction coordinator
- Use REST APIs for communication
- Share a centralized database
- Implement message queues
To ensure the consistency and integrity of data across different microservices in a microservices-based application, implementing a distributed transaction coordinator (Option 1) is a suitable approach. This coordinator can manage transactions across multiple microservices, ensuring that Create and Update operations either succeed or fail together, preserving data integrity. Using REST APIs (Option 2) for communication is a common practice but doesn't guarantee transactional consistency. Sharing a centralized database (Option 3) can create tight coupling and hinder the benefits of microservices. Implementing message queues (Option 4) helps with asynchronous communication but doesn't inherently guarantee data consistency across microservices.
When designing a schema for a SQL database in Node.js, the ______ key is used to establish a relationship between two tables.
- Foreign
- Index
- Primary
- Composite
When designing a schema for a SQL database in Node.js, the Foreign Key is used to establish a relationship between two tables. It creates a link between a field in one table and the primary key of another table, enabling data integrity and referential integrity.
What is the significance of test coverage in a codebase, and how does it impact the development process?
- Test coverage measures the number of lines of code tested; High test coverage guarantees a bug-free codebase; Test coverage is irrelevant for development.
- Test coverage measures the percentage of code executed by tests; It helps identify untested code paths and potential bugs; High test coverage is a valuable metric but doesn't guarantee bug-free code.
- Test coverage measures the number of test cases written; High test coverage means exhaustive testing and zero defects; Test coverage should be minimized to save development time.
- Test coverage is the number of test tools used; High test coverage indicates a comprehensive testing suite; Test coverage depends on project size.
Test coverage measures the percentage of code executed by tests. It helps identify untested code paths, improving code quality. However, it does not guarantee a bug-free codebase, as it depends on the quality of the tests. The other options provide inaccurate definitions or misconceptions about test coverage.
When creating a custom error class in Express.js, it should extend the built-in ______ class.
- Error
- HttpException
- AppError
- CustomError
When creating a custom error class in Express.js, it should extend the built-in Error class. This allows you to leverage the error handling capabilities provided by JavaScript and Express.js. Extending other classes like HttpException, AppError, or CustomError is not a standard practice for custom error classes in Express.js.
In the http module, the ______ event of the server object is emitted when the server closes.
- close
- end
- disconnect
- terminate
In the http module, the close event of the server object is emitted when the server closes. This event allows you to perform cleanup or take action when the server is shutting down. The other options (end, disconnect, terminate) do not represent the server closing event in the HTTP module.
The for…of statement creates a loop iterating over ________ objects in JavaScript.
- enumerable
- all
- array-like
- visible
The for...of statement in JavaScript creates a loop that iterates over array-like objects, which include arrays, strings, maps, sets, and other objects that have iterable properties. It's particularly useful for iterating over the values of such objects.
In Node.js, the Event Loop operates on a single ________, which makes it suitable for I/O-bound tasks.
- Thread
- Core
- Process
- Module
In Node.js, the Event Loop operates on a single Core, not a thread or process. This single-threaded event loop design is one of the key features of Node.js, making it suitable for I/O-bound tasks as it can efficiently handle asynchronous operations without the overhead of multiple threads or processes.
The concept of defining a blueprint for the data in the database is known as ________.
- Schema
- Query
- Index
- Aggregate
The concept of defining a blueprint for the data in the database is known as "Schema." A schema defines the structure, relationships, constraints, and integrity rules of the data stored in a database.
When an EventEmitter instance experiences an error, the typical event that is emitted is ______.
- 'error'
- 'exception'
- 'fail'
- 'warning'
In Node.js, when an EventEmitter instance experiences an error, the typical event that is emitted is 'error'. This event allows you to handle errors that occur within event listeners attached to the EventEmitter.