Nonvalid Uses of UPDATE
An UPDATE operation causes an error message to be returned when any of the following
conditions occur:
The operation attempts to update a field using a value that violates a constraint
(for example, UNIQUE or referential) declared for the column.
The operation attempts to update a field using a value that is of a different numeric
type than that declared for the column and the value cannot be converted correctly
to the correct type.
The operation attempts to update a VARCHAR column, and that operation causes the row
to become identical to another row (except for the number of trailing pad characters),
for a table not permitting duplicate rows.
The operation attempts to update a CHARACTER column with a value that is not in the
repertoire of the destination character data type.
If in ANSI session mode, updating character data, where in order to comply with maximum
length of the target column, non-pad characters are truncated from the source data.
This update is valid in Teradata session mode.
The operation attempts to update a row by using values that will create a duplicate
of an existing row, for a table not allowing duplicate rows.
The operation references objects in multiple databases without using fully‑qualified
names. Name resolution problems may occur if referenced databases contain tables or
views with identical names and these objects are not fully qualified. Name resolution
problems may even occur if the identically named objects are not themselves referenced.
A JSON entity reference was used in the target portion of the SET clause.