Difference between Subquery and Correlated Subquery

Question

Is the following piece of SQL Query a normal query or a Correlated Subquery ??

SELECT UserID,
       FirstName,
       LastName,
       DOB,
       GFName,
          


        

Answer 1

In an SQL query, if the inner query executes for every row of the outer query. If the inner query is executed for once and the result is consumed by the outer query, then it is called as non co-related query.

Correlated sub-queries usually correspond to normal join queries, i.e. join queries that have no sub-queries, and can usually be expressed as such. It is sometimes recommended that they are translated into such join queries, because most SQL DBMSs will execute them .....