Tags for Nulls
unable to cast object of type 'system.dbnull' to type 'system.string'
We have a query that we know will return nulls for a certain column.  However, in the result set, sometimes we see null and sometiems it returns <Error> in the column when the value should be null.   When I hover over the <Error> value, the below message is displayed.  
Nulls error
Solving Business Problems with SQL
The presentation is to acquaint business users with Structured Query Language (SQL) and some interesting techniques to access their data with examples for using CASE; Subqueries and Correlated Subqueries; Types of SQL joins and how they are implemented on Teradata; facts about NULLs; Derived Table usage and other interesting optimizer information.
sql joins dml case Nulls