What is a Sub-Query, in MS SQL Server?

Answer 1

Sub query: is the secondary query in a query.
ex: select col1,col2 from (select scol1 as col1,scol2 as col2 from sub_query_tbl) as a
the query in paranthesis is sub query , in subquery no order by should use.
there are diff types of sub queries exists,
independent sub query, correlated sub query,single valued,multi valued