Is it possible to rewrite queries with EXISTS/NOT EXISTS without using these operators? What types of JOINs do you know?

Yes, queries with EXISTS/NOT EXISTS can be rewritten without these operators by using JOINs and aggregate functions.

For example, a query with EXISTS:

SELECT * FROM A WHERE EXISTS (SELECT 1 FROM B WHERE B.a_id = A.id);

Can be rewritten using INNER JOIN:

SELECT DISTINCT A.* FROM A INNER JOIN B ON B.a_id = A.id;

For NOT EXISTS, you can use LEFT JOIN with a NULL check:

SELECT A.* FROM A LEFT JOIN B ON B.a_id = A.id WHERE B.a_id IS NULL;

Main types of JOINs:

• INNER JOIN — returns rows that match in both tables.
• LEFT JOIN (LEFT OUTER JOIN) — returns all rows from the left table and matching rows from the right, or NULL if there are no matches.
• RIGHT JOIN (RIGHT OUTER JOIN) — the opposite, all from the right and matching from the left.
• FULL JOIN (FULL OUTER JOIN) — combines LEFT and RIGHT JOIN, returning all rows from both tables.

Understanding these JOINs helps in rewriting and optimizing queries.