Rules for Using the DEFAULT Function With Update - Teradata Database - Teradata Vantage NewSQL Engine

SQL Data Manipulation Language
Product
Teradata Database
Teradata Vantage NewSQL Engine
Release Number
16.20
Published
March 2019
Language
English (United States)
Last Update
2019-05-03
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B035-1146
lifecycle
previous
Product Category
Teradata Vantage™
The following rules apply to using the DEFAULT function with an UPDATE statement:
  • The DEFAULT function takes a single argument that identifies a relation column by name. The function evaluates to a value equal to the current default value for the column. For cases where the default value of the column is specified as a current built-in system function, the DEFAULT function evaluates to the current value of system variables at the time the request is executed.

    The resulting data type of the DEFAULT function is the data type of the constant or built-in function specified as the default unless the default is NULL. If the default is NULL, the resulting date type of the DEFAULT function is the same as the data type of the column or expression for which the default is being requested.

  • The DEFAULT function has two forms. It can be specified as DEFAULT or DEFAULT (column_name). When no column name is specified, the system derives the column based on context. If the column context cannot be derived, the request aborts and an error is returned to the requestor.
  • You can specify a DEFAULT function without a column name argument as the expression in the SET clause. The column name for the DEFAULT function is the column specified as the column_name. The DEFAULT function evaluates to the default value of the column specified as column_name.
  • You cannot specify a DEFAULT function without a column name argument as part of the expression. It must be specified by itself. This rule is defined by the ANSI SQL:2011 specification.
  • You can specify a DEFAULT function with a column name argument in the source expression. The DEFAULT function evaluates to the default value of the column specified as the input argument to the DEFAULT function.

    For example, DEFAULT(col2) evaluates to the default value of col2. This is a Teradata extension to the ANSI SQL:2011 specification.

  • You can specify a DEFAULT function with a column name argument anywhere in an update expression. This is a Teradata extension to the ANSI SQL:2011 specification.
  • When no explicit default value has been defined for a column, the DEFAULT function evaluates to null when that column is specified as its argument.

See Teradata Vantage™ SQL Functions, Expressions, and Predicates, B035-1145 for more information about the DEFAULT function.