Is it secure to set default value for password field?
I see only 2 options to get it to work :


Application inserts value for password field
Table has NULL or default value for password field


If the column allows NULL, that should be enough, right?
If you want it to have a value, having the application insert it, across the network, is probably riskier, than setting a default value in the table.

Setting the same default value for all users may also pose a slight risk (someone gets a hold of the hash and tries to reverse-engineer). If you want to avoid that too, you can use a BEFORE trigger to set a computed default value based on username+timestamp as salt for the encrypted password field.