Q1. What is the $lookup stage and what are its trade-offs?
$lookup performs a left outer join against another collection in the same database. The basic form matches localField against foreignField and returns matches in an "as" ...
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Q2. 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...
Q3. What are different JOINs in SQL?
1. **INNER JOIN** — matching rows only 2. **LEFT (OUTER) JOIN** — all left + matched right 3. **RIGHT (OUTER) JOIN** — all right + matched left 4. **FULL OUTER JOIN** — a...
Q4. Which is NOT TRUE about the ON clause?
The `ON` clause specifies the join condition. It improves readability over the old comma-syntax, supports multi-column joins (`ON a.id = b.id AND a.type = b.type`), and i...
Q5. Can you join 3 tables with INNER JOIN?
Yes. There's no practical limit (though performance degrades with many joins). ```sql SELECT f.name, d.name AS division, c.name AS country FROM faculty f INNER JOIN divis...
Q6. Advantages of views?
1. **Simplify complex queries** — hide JOINs and aggregations 2. **Security** — expose only specific columns/rows 3. **Logical independence** — shield apps from schema ch...