What is correlated subquery in SQL with example?

In a SQL database query, a correlated subquery (also known as a synchronized subquery) is a subquery (a query nested inside another query) that uses values from the outer query. Because the subquery may be evaluated once for each row processed by the outer query, it can be slow.

What is correlated subquery w3schools?

A query is called correlated subquery when both the inner query and the outer query are interdependent. For every row processed by the inner query, the outer query is processed as well. The inner query depends on the outer query before it can be processed.

What is a correlated sub-query write an example query?

EXAMPLE of Correlated Subqueries : Find all the employees who earn more than the average salary in their department. SELECT last_name, salary, department_id FROM employees outer WHERE salary > (SELECT AVG(salary) FROM employees WHERE department_id = outer.department_id);

What is the difference between a correlated query and nested query?

In Nested query, a query is written inside another query and the result of inner query is used in execution of outer query. In Correlated query, a query is nested inside another query and inner query uses values from outer query. There is no Inner Query or Outer Query.

What are correlated queries in SQL?

A SQL correlated subquery is a query which is executed one time for each record returned by the outer query. It is called correlated as it is a correlation between the number of times the subquery is executed with the number of records returned by the outer query (not the subquery).

What is the difference between a correlated subquery and a non correlated subquery?

A non-correlated subquery is executed only once and its result can be swapped back for a query, on the other hand, a correlated subquery is executed multiple times, precisely once for each row returned by the outer query.

What is correlated subquery and how it differ from sub query?

In Nested query, a query is written inside another query and the result of inner query is used in execution of outer query. In Correlated query, a query is nested inside another query and inner query uses values from outer query. There is no Inner Query or Outer Query. Hence, no dependency is there.

What do you mean by correlated subquery in database?

– A correlated subquery, however, executes once for each row considered by the outer query. – In other words, the inner query is driven by the outer query. – The correlated subquery in the example above is marked in red.

Which is a feature of a correlated subquery?

A correlated subquery is a SELECT statement nested inside another T-SQL statement, which contains a reference to one or more columns in the outer query. Therefore, the correlated subquery can be said to be dependent on the outer query. This is the main difference between a correlated subquery and just a plain subquery.

What is correlated query?

In a SQL database query, a correlated subquery (also known as a synchronized subquery) is a subquery (a query nested inside another query) that uses values from the outer query. Because the subquery may be evaluated once for each row processed by the outer query, it can be slow.

What is sub in SQL?

SQL Sub queries are the queries which are embedded inside another query. The embedded queries are called as INNER query & container query is called as OUTER query. The subqueries are the queries which are executed inside of another query. The result SQL query totally depends on the result of a subquery.