Q11. What is the difference between a primary key and a foreign key?
A primary key uniquely identifies each row in a table. It must be unique and not null, and a table has at most one. It may be a single column or a composite of several, a...
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Q12. What is the difference between TCP and UDP?
TCP and UDP are transport-layer protocols with opposite trade-offs. TCP is connection-oriented. It sets up a connection with a three-way handshake, numbers every segment,...
Q13. What is the difference between a process and a thread?
A process is a running program with its own virtual address space, code, data, heap, open file descriptors and at least one thread. The operating system isolates processe...
Q14. What are the four pillars of object-oriented programming?
Object-oriented programming rests on four pillars: - Encapsulation: keep state private and expose behaviour through methods, so invariants cannot be broken from outside. ...
Q15. What is a cohort retention analysis?
Cohort analysis groups users by a shared start event, usually their first activity period, and tracks behaviour over subsequent periods. Retention is the share of a cohor...
Q16. Explain p-value and statistical significance to a non-technical stakeholder.
Imagine we assume a change has no real effect, which is the null hypothesis. The p-value answers: if that were true, how surprising would the data we observed be? A p-val...
Q17. What is the bias-variance tradeoff?
Bias is error from overly simple assumptions; a high-bias model underfits and misses patterns in both training and test data. Variance is error from sensitivity to the tr...
Q18. Explain the difference between a data lake and a data warehouse.
A data warehouse stores structured, modelled data optimized for analytics and SQL. It uses schema-on-write: data is cleaned and conformed before loading, typically into s...
Q19. What are the Redis data structures and what is each used for?
Redis exposes several core data types, each with tailored commands. - Strings: counters, cached serialized objects and rate limiters using INCR and SETEX. - Hashes: objec...
Q20. How does MongoDB differ from a relational database?
MongoDB is a document database. Data is stored as flexible BSON documents inside collections instead of rows in tables with a fixed schema. Each document can have its own...