Not Null

Keyword NOT NULL

IS NOT NULL operator

You can use IS NOT NULL operator to check if value is NULL(undefined).

IF OBJECT_ID('dbo.Parts') IS NOT NULL
  DROP TABLE dbo.Parts;
GO

NOT NULL column constraint

AlaSQL supports NOT NULL column constraints.

Please see this example:

CREATE TABLE dbo.Cities (
  cityid  CHAR(3)     NOT NULL PRIMARY KEY,
  city    VARCHAR(30) NOT NULL,
  region  VARCHAR(30) NULL,
  country VARCHAR(30) NOT NULL
);

See also: NULL, undefined