If you say in SQL query SELECT runs first then you are wrong

Description:
Even though you write SELECT first, the database executes it last.
Comment "Pdf" for detailed notes pdf.

This is the actual order SQL follows:

⸻

1️⃣ FROM
The database decides which tables to read and how to join them.

2️⃣ WHERE
Rows that don’t match the condition are filtered out.

3️⃣ GROUP BY
Remaining rows are grouped into buckets.
Used for aggregations like totals, counts, and averages.

4️⃣ HAVING
Filters groups after aggregation is done.
Unlike WHERE, this works on grouped results.

5️⃣ SELECT
Final columns and calculations are produced.
Aliases and computed fields are evaluated here.

6️⃣ ORDER BY
The result set is sorted.
Sorting happens late because it’s expensive.

7️⃣ LIMIT / OFFSET
Only the requested number of rows are returned.
Everything else is discarded.

⸻

Interview takeaway:
SQL is optimized to filter early, compute late, and return last - that’s why execution order matters more than query order.

(SQL execution order, SQL query optimization, database internals, SQL interview questions, backend engineering, system design basics, SQL performance, relational databases)

#SQL #BackendEngineering #DatabaseDesign #SystemDesign #ProgrammingTips

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