Question about NULL values in SQL
NULL means that there is no value for that column of the record and it does not equal anything. So in both of your queries nothing can equal NULL.

Wiki Entry on Null


  The Greek lowercase omega (ω) character is used to represent Null in database theory.
  Null (or NULL) is a special marker used in Structured Query Language to indicate that a data value does not exist in the database. Introduced by the creator of the relational database model, E. F. Codd, SQL Null serves to fulfil the requirement that all true relational database management systems (RDBMS) support a representation of "missing information and inapplicable information". Codd also introduced the use of the lowercase Greek omega (ω) symbol to represent Null in database theory. In SQL, NULL is a reserved word used to identify this marker.