SqlServer series notes-subquery
The meaning of sub-query:
Use a query statement as a result set for other SQL statements to use, just like using a normal table
Query statements that are treated as result sets are called subqueries
Almost all places where tables can be used can be replaced by subqueries.
Key child IN
Exists Not Exists subquery returns true or false
SELECT * FROM (SELECT * FROM T2 where FAge
