Q31. How do you model a one-to-many relationship in MongoDB?
The answer depends on the size of the "many" side and the access pattern. One-to-few: embed an array of subdocuments. A user with a handful of addresses embeds them, so o...
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Q32. How do you keep a cache consistent with the database?
Perfect consistency is not achievable without giving up caching; aim for bounded staleness and correct behavior. Practical rules: - On write, commit to the database first...
Q33. Which are valid SQL keywords?
`SELECT`, `FROM`, `WHERE`, `GROUP BY`, `HAVING`, `ORDER BY`, `JOIN`, `INSERT`, `UPDATE`, `DELETE`, `CREATE`, `ALTER`, `DROP`, `INDEX`, `UNION`, `LIMIT`, `DISTINCT`, `AS`,...
Q34. Explain slowly changing dimensions and SCD Type 2.
Dimensions change over time: a customer moves city, a product changes category. A slowly changing dimension strategy decides how history is preserved. - Type 1: overwrite...
Q35. Which are valid SQL comments?
SQL supports both single-line and multi-line commenting syntax across relational database engines: ### 1. Single-Line Standard Comment (`--`): The official ANSI SQL stand...
Q36. What is the medallion architecture?
The medallion architecture organizes a lakehouse into three refinement layers. - Bronze (raw): data landed as-is from sources, append-only, with ingestion metadata. It is...
Q37. Which SQL statement extracts data?
`SELECT`. Optional clauses: `WHERE`, `GROUP BY`, `HAVING`, `ORDER BY`, `LIMIT`, `JOIN`. ```sql SELECT name AS full_name, salary * 12 AS annual_salary FROM employees WHERE...
Q38. How would you design a change data capture pipeline?
CDC captures row-level changes from a source database and streams them downstream with low latency. A typical design: - Capture: read the database transaction log with a ...
Q39. How to select all records from table Products?
```sql SELECT * FROM products; ``` ⚠️ *Interview tip*: Always follow up with "But in production, I list explicit columns to reduce network overhead and prevent breaking i...
Q40. Can we rename a column in output?
Yes, using `AS` (alias): ```sql SELECT first_name AS fname, last_name AS lname FROM customers; -- AS is optional but recommended for readability: SELECT first_name fname ...