All this discussion about the definition of NULL and its use in
database querying has been most interesting and enlightening. I
hadn't realized I was asking such a deep question. Unfortunately, I'm
still at the stage of designing tables where I KNOW I will be loading
thousands of records that, more often than not, contain anywhere from
10% to 50% columns where no values have been entered for whatever
reason (exporting an existing Lotus Notes database to MySQL).
Naturally, that 10-50% will never consist of precisely the same
columns from one record to the next.
Putting aside issues about the distinctions among NULL, 0, and "", my
question is this: At the end of the day, which system is going to be
easier to export to and which will be faster (produce result sets
faster) when all the data are loaded? There are three formats for the
DDL that I can think of immediately (I'm a newbie at this stuff):
1. CREATE TABLE My_Table(
First_Field VARCHAR(10), ..., ...)
2. CREATE TABLE My_Table(
First_Field VARCHAR(10) NOT NULL, ..., ...)
3. CREATE TABLE My_Table(
First_Field VARCHAR(10) NOT NULL Default '', ...,...)
As I read it, each of the above results in a different table. (BTW,
it
looks like using the MySQLCC GUI table builder results in format 3.)
The MySQL documentation says that tables with non-nullable columns
yield better performance. What does that mean if you have all NOT
NULL
columns (assume for discussion that everything is a character), many
of which contain "" as a value?
Randy
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