Create a table with NOT NULL DEFAULT''""

Is that we don’t want nulls in the table

So why you do not want to appear too:
for future look-up table or easy match because null comparison is relatively Find some difficulty,
null as a type, more time to use special symbols: is null / is not null
encounter All other operators return null

And the efficiency is not high, which is not conducive to improving the efficiency of the index

So we don’t want it to be null and define it as other things such as ”0 0.00, etc.