7. Understanding Database Procedures, Sessions, and Events : How Database Procedures Are Created, Invoked, and Executed : Table Procedure : Table Procedure Restrictions
 
Table Procedure Restrictions
The parameter list of a table procedure can reference columns from tables in the FROM clause or result columns of another table procedure in the FROM clause. This effectively represents a join between the tables and table procedures with one set of result rows being produced by the table procedure for each set of column values referenced in its parameter list. However, if parameter lists of table procedures reference result columns of other table procedures, they must not form a cycle.
For example, the following is not permitted
FROM tproc1(p1 = 25, p2 = tp2.rc1) tp1, tproc2(q1 = tp1.rc4, q2 = 'abc') tp2, ...
because the tproc1 parameter list references a result column of tproc2 and the tproc2 parameter list references a result column from tproc1.
Note:  The LOB result column of a table procedure cannot be referenced in a query. A syntax error will result.