Related subqueries "SQL Server"

Inquire about books in book tables that are larger than the average price of such books

First record the class number of the value of 2 into the subquery, the subquery is

Select AVG (Price)

From book B

where b.id=2

The average price for a book with class number 2 is (23+45)/2=34

and make judgments with external queries.

SELECT * FROM Book a

where price>34

And then class number 3 in the book again by comparing

Correlated subqueries (multi-valued subqueries)

1. A non-correlated subquery (nested subquery) is an external subquery that executes only once, the query can be executed multiple times, and the value is passed to the external query after execution.

2. In the related subquery, the outer query executes once, and the subquery executes once

Related subqueries "SQL Server"