15.00 - NULL Keyword as a Literal - Teradata Database

Teradata Database SQL Fundamentals

prodname
Teradata Database
vrm_release
15.00
category
Programming Reference
featnum
B035-1141-015K

NULL Keyword as a Literal

A null represents either:

  • An empty column
  • An unknown value
  • An unknowable value
  • Nulls are neither values nor do they signify values; they represent the absence of value. A null is a place holder indicating that no value is present.

    NULL Keyword

    The keyword NULL represents null, and is sometimes available as a special construct similar to, but not identical with, a literal.

    ANSI Compliance

    NULL is ANSI/ISO SQL:2011-compliant with extensions.

    Using NULL as a Literal

    Use NULL as a literal in the following ways:

  • A CAST source operand, for example:
  •       SELECT CAST (NULL AS DATE);
  • A CASE result, for example.
  •       SELECT CASE WHEN orders = 10 THEN NULL END FROM sales_tbl;
  • An insert item specifying a null is to be placed in a column position on INSERT.
  • An update item specifying a null is to be placed in a column position on UPDATE.
  • A default column definition specification, for example:
  •       CREATE TABLE European_Sales
             (Region INTEGER DEFAULT 99
             ,Sales Euro_Type DEFAULT NULL);
  • An explicit SELECT item, for example:
  •       SELECT NULL

    This is a Teradata extension to ANSI.

  • An operand of a function, for example:
  •       SELECT TYPE(NULL)

    This is a Teradata extension to ANSI.

    Data Type of NULL

    When you use NULL as an explicit SELECT item or as the operand of a function, its data type is INTEGER. In all other cases NULL has no data type because it has no value.

    For example, if you perform SELECT TYPE(NULL), then INTEGER is returned as the data type of NULL.

    To avoid type issues, cast NULL to the desired type.

    Related Topics

    For information on the behavior of nulls and how to use them in data manipulation statements, see “Manipulating Nulls” on page 141.