Robert Mark (10/30/2014)

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I have two other considerations for NULL vs NOT NULL.

1) If you're application coding language requires checking for null values when you read in data from the database, this is a lot of extra coding and is a good reason to have NOT NULL columns.

2) Use of default values for columns. To avoid needing NULL values, it is easy to set a default value for every field in a table, this allows you to not need to check for NULL values in your application for most queries (except for some aggregate or outer join queries). So a numeric field can be defaulted to 0, a date to a specific date in the past or future, a string to a blank value or

'Unassigned', or 'Not Specified', etc.

So using NOT NULL columns with default values keeps your database clean and the data within the tables predictable for your application. I know that default values can slow down insert operations, but for most applications this is not an issue.