Question

If this question is too broad, my apologies. I am a DBA and I am working with a developer that thinks column defaults are a bad idea and that just setting the column to disallow nulls is good enough.

I am looking for the benefits of column defaults from the developers point of view. Thank you for your comments.

Answer 1

Column defaults allow you to remove a lot of the hassle of creating records from your code or application logic.

Advantage #1: If you have a table with 2 columns of user information and 20 columns of tinyint/boolean fields, let’s say they are privacy settings, and you go to create a new record in that table, without a DEFAULT value you’re going to have to specify every column in your query. There’s probably a common setup that you want these records to have by default, and you can set this up using DEFAULT values. When you INSERT a record, you only need to specify the two user information fields, and voila, your record is created with a nice set of common privacy settings. You can tweak the flags individually after that.

Advantage #2: Forward compatibility! If you have a bunch of INSERTs in your code, and then some columns are added on, you’re going to have to go back and modify all those INSERTs if you don’t specify a DEFAULT value (assuming, as is common, that NULLs aren’t going to cut it). Often it isn’t necessary to update old code for a new column (since the old code by nature doesn’t care about the new column), so this would be a huge pain in the @$$ if you had to start going back and handling every new column in your code as it came along.