The data type of the LEAD or LAG function's returned values is the same as the specified value of value_expression. If default_value_expression and value_expression have different data types, Teradata recommends explicitly casting default_value_expression to the data type of value_expression.
In ANSI mode, an error occurs if default_value_expression and value_expression data types do not match.
In the Teradata Transaction (BTET) mode, if the data types do not match, the database attempts to cast the default_value_expression to the value_expression data type based on the internal casting rules. If this results in casting rule violations, an error message displays.