Nested queries and Correlated sub-queries are both different. Try to understand these with examples
Nested Queries
A subquery can contain another query, making it a query with multiple nested subqueries.
SELECT customer.*
FROM customer
WHERE c_no IN
(SELECT c_no
FROM c_order
WHERE p_code IN
(SELECT p_code FROM product WHERE p_name NOT LIKE '%Nut%'
)
);
My analysis
- All the nested SQL queries run in sequence to get the result
Co-related sub-query
A subquery can also be related to its outer query, where one or more columns from the outer query table are related to the column(s) of the subquery table in the WHERE clause of the subquery. This type of subquery is called the correlated subquery.
SELECT customer.*
FROM customer
WHERE c_no IN
(SELECT c_no
FROM c_order o
JOIN product p
ON o.p_code = p.p_code
WHERE p_name NOT LIKE '%Nut%'
AND customer.c_no = o.c_no
);My analysis
- A correlated subquery has a dependency on the outer query
Srinimf 