When to use NULL in MySQL tables

Question

I appreciate the semantic meaning of a NULL value in a database table, different from both false and the empty string \'\'. However, I have often read about performance pro

Answer 1

We don't allow NULL values in our databases unless it's for numeric values, or for dates. The reason why we do this is because numeric values sometimes should not be defaulted to zero as this is very, very bad. I'm a developer for a stock brokers and there's a big, big difference between NULL and 0. The use of COALESCE comes in handy if we do want to default values back to zero even though we don't store them as such.

MyVal = COALESCE(TheData, 0)

As we do bulk inserts of data from flat files we use format files to determine the entry of the data which automagically converts empty values into blank strings anyway.

Dates default to whatever value may appear dependant on the collation I believe, but ours default to something like 1900, and again, dates are extremely important. Other plain text values aren't so important, and if left blank typically qualify as okay.