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Schema: NULL columns

Applies to ✅ Open Source Edition   ✅ Express Edition   ✅ Professional Edition   ✅ Enterprise Edition

In most RDBMS, the default nullability on any column is NULL, even if NOT NULL is mostly a more reasonable default. Whenever you know your data is not supposed to contain NULL values, then add an explicit NOT NULL constraint. This has the following benefits:

  • Data integrity: One case of incorrect data less to worry about.
  • Documentation: Even if your client application might make sure you'll never get NULL values in a column, it's still better to formally communicate this fact through a constraint.
  • Performance: With NULL being an impossible value, quite a few optimisations can be applied that couldn't be, otherwise.

For example

CREATE TABLE customer (
  -- [...]
  phone   TEXT,          -- Here, the default of being nullable applies (in most RDBMS), but should it?
  address TEXT NULL,     -- The address might optional, you can mark it as such, explicitly, in many RDBMS
  email   TEXT NOT NULL  -- Every customer needs an email, this isn't an optional field

This rule obviously doesn't apply when a value is optional, in case of which NULL might be a desirable value.


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