Validating SQL expressions

Question

Hello,
Am researching a way for validating SQL expressions.
Say I have expressions substr(<tname.coumn_name>,1,2), I want to parse this expression for completeness, meaning whether the expression can be used in a case, decode or a normal select statement as a where clause.
Is there any functionality available within oracle to achieve this or any pointer to some sample PL/SQL code to achieve this is welcome.
TIA,
Prakash. T

Answer 1

If all we want to do is parsing, without creating a plan_table of any kind and without writing to it, we can use dbms_sql.
SQL> var s varchar2(100)
SQL> exec :s := 'select substr(dummy,1,1) from dual'
PL/SQL procedure successfully completed.
SQL> declare
  2    l_c pls_integer;
  3  begin
  4    l_c := dbms_sql.open_cursor;
  5    dbms_sql.parse(l_c, :s, dbms_sql.native);
  6  end;
  7  /
PL/SQL procedure successfully completed.
SQL> exec :s := 'select substrx(dummy,1,1) from dual'
PL/SQL procedure successfully completed.
SQL> /
declare
ERROR at line 1:
ORA-00904: "SUBSTRX": invalid identifier
ORA-06512: at "SYS.DBMS_SYS_SQL", line 826
ORA-06512: at "SYS.DBMS_SQL", line 39
ORA-06512: at line 5It is after all only one additional variable declaration and an extra line of code.