Constructor of nested table subtype

Question

The following code gives me an error PLS-00355: use of pl/sql table not allowed in this context (I checked in 11.2.0.2.0):
DECLARE
  TYPE    t_number_tab     IS TABLE OF NUMBER;
  SUBTYPE t_number_tab_sub IS t_number_tab;
  v_sub t_number_tab_sub;
BEGIN
  -- throws "PLS-00355: use of pl/sql table not allowed in this context":
  v_sub := t_number_tab_sub();
END;I looked in docs and can't find a reason why this doesn't work. I know I can initialize v_sub with t_number_tab(), but I would like to know why my example above doesn't work.

Answer 1

Welcome to the forum!
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The following code gives me an error PLS-00355: use of pl/sql table not allowed in this context (I checked in 11.2.0.2.0):
DECLARE
  TYPE    t_number_tab     IS TABLE OF NUMBER;
  SUBTYPE t_number_tab_sub IS t_number_tab;
  v_sub t_number_tab_sub;
BEGIN
  -- throws "PLS-00355: use of pl/sql table not allowed in this context":
  v_sub := t_number_tab_sub();
END;I looked in docs and can't find a reason why this doesn't work. I know I can initialize v_sub with t_number_tab(), but I would like to know why my example above doesn't work.
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You haven't really defined a subtype; just a different name for the type.
Subtypes have to be based on scalar types. See the PL/SQL Language doc
http://docs.oracle.com/cd/E11882_01/appdev.112/e10472/datatypes.htm#CHDEAFDJ
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PL/SQL lets you define your own subtypes. The base type can be any scalar PL/SQL type, including a previously defined user-defined subtype.
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Even though the compiler seems to allow it you have the equivalent of an 'unconstrained' subtype which is just another name for the type
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Unconstrained Subtypes
An unconstrained subtype has the same set of values as its base type, so it is only another name for the base type.
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Since all you have changed is the name you still have to use the constructor for the actual type: t_number_tab()