There are manby things which are considered as basics in dot net nuke.When you are using host sql window from dnn then most definitely you will need to have ideas of basic sql statements to fetch info from db.Few of them are:-

Listing all tables from DataBase:-

SELECT * FROM information_schema.Tables

Get Stored procedure description and Structure:-

select * from information_schema.routines where routine_name = ‘Stored Procedure Name’

Querry to fetch all tables in a database:

select * from sysobjects where type=’u’

Querry to fetch all procedures in a database:

select * from sysobjects where type=’p’

Display Table Creation And Owner info

sp_help table_name

Display Table structure and columns:-

sp_columns @table_name = ‘table_name‘

this will show all fields from table table_name including data type and length information.

Return a list of objects that can be queried in the current environment

EXEC sp_tables

Return information about the syscolumns table in the Company database

EXEC sp_tables syscolumns, dbo, Company, "'SYSTEM TABLE'"

Altering/modifying cloumn Width :-
alter table table_name ALTER COLUMN column_name varchar(30)