Questions about SQL: JOINs, the order of logical execution of SELECT queries.

JOIN is an operation that combines tables based on a specific condition. Main types of JOIN:

• INNER JOIN — returns rows where there are matches in both tables.
• LEFT JOIN — returns all rows from the left table and matching rows from the right; if there is no match, NULLs are used.
• RIGHT JOIN — the opposite, all from the right and matching from the left.
• FULL JOIN — combines all rows from both tables, filling NULLs where there are no matches.

The logical order of executing a SELECT query:

1. FROM — selecting tables and performing JOINs.
2. WHERE — filtering rows.
3. GROUP BY — grouping data.
4. HAVING — filtering groups.
5. SELECT — selecting columns.
6. DISTINCT — removing duplicates.
7. ORDER BY — sorting.
8. LIMIT/OFFSET — limiting the number of rows.

Understanding this order helps in writing efficient and correct queries.