Cause: The expression does not designate
a variable that can have a value assigned to it. For example, the function
SYSDATE cannot appear on the left hand side of an assignment statement such as
SYSDATE := `01-JAN-1990`;
Action: Correct the illegal assignment
statement.

Relared Errors:
PLS-00322:
declaration of a constant `string` must contain an initialization
assignme
PLS-00323:
subprogram or cursor `string` is declared in a package specification
and m
PLS-00324:
cursor attribute may not be applied to non-cursor
`string`
PLS-00325:
non-integral numeric literal string is inappropriate in this
context
PLS-00326: IN
clause must contain same number of expressions as subquery
PLS-00327:
string is not in SQL scope here
PLS-00328: A
subprogram body must be defined for the forward declaration of
string.
PLS-00329:
schema-level type has illegal reference to string
PLS-00330:
invalid use of type name or subtype name
PLS-00331:
illegal reference to string