Q11. 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...
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Q12. 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`,...
Q13. 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...
Q14. 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...
Q15. 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...
Q16. 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 ...
Q17. How to select FirstName from Customers?
To retrieve only the `FirstName` column from the `Customers` table, use the standard `SELECT` projection statement: ```sql SELECT FirstName FROM Customers; ``` ### Perfor...
Q18. What does the FROM clause do?
The **`FROM`** clause identifies the source table(s), views, joined tables, or subqueries from which data is to be retrieved, filtered, and aggregated. ### Logical SQL Pr...
Q19. Which statement returns only different values?
`SELECT DISTINCT`. It operates on the *entire selected row*. ```sql -- Returns unique city-state combinations SELECT DISTINCT city, state FROM addresses; ```
Q20. Display distinct cities in ADDRESSES(id, street_name, number, city, state)?
To retrieve a list of unique cities without duplicates from the `ADDRESSES` table, use the **`DISTINCT`** keyword: ```sql SELECT DISTINCT city FROM addresses ORDER BY cit...