why we use subquery in sql code example

Example 1: what is subquery in sql

SUBQUERY IS NESTED QUERY INSIDE A SELECT, 
INSERT OR UPDATE METHODS. OR INSIDE ANOTHER SUBQUERY

Example 2: why we use subquery in sql

We use subquery in order to get aggregate value in column without grouping data

Example 3: subquery sql

UPDATE Book SET note= 'editore: ' + (SELECT name FROM Publisher WHERE Publisher.ID = Book.publisher)