Question

This is my use case: Input is a string representing an Oracle PL/SQL statement of arbitray complexity. We may assume it’s a single statement (not a script).
Now, several bits of this input string have to be rewritten.

E.g. table names need to be prefixed, aggregate functions in the selection list that don’t use a column alias should be assigned a default one:

SELECT SUM(ABS(x.value)), 
TO_CHAR(y.ID,'111,111'),
y.some_col
FROM
tableX x,
(SELECT DISTINCT ID
FROM tableZ z
WHERE ID > 10) y
WHERE
...

becomes

SELECT SUM(ABS(x.value)) COL1, 
TO_CHAR(y.ID,'111,111') COL2,
y.some_col
FROM
pref.tableX x,
(SELECT DISTINCT ID, some_col
FROM pref.tableZ z
WHERE ID > 10) y
WHERE
...

(Disclaimer: just to illustrate the issue, statement does not make sense)

Since aggregate functions might be nested and subSELECTs are a b_tch, I dare not use regular expressions. Well, actually I did and achieved 80% of success, but I do need the remaining 20%.

The right approach, I presume, is to use grammars and parsers.
I fiddled around with c++ ANTLR2 (although I do not know much about grammars and parsing with the help of such). I do not see an easy way to get the SQL bits:

list<string> *ssel = theAST.getSubSelectList(); // fantasy land

Could anybody maybe provide some pointers on how “parsing professionals” would pursue this issue?
EDIT: I am using Oracle 9i.

Answer 1

Maybe you can use this, it changes an select statement into an xml block:

declare
    cl clob;
begin
    dbms_lob.createtemporary (
        cl,
        true
    );
    sys.utl_xml.parsequery (
        user,
        'select e.deptno from emp e where deptno = 10',
        cl
    );
    dbms_output.put_line (cl);
    dbms_lob.freetemporary (cl);
end;
/ 

<QUERY>
  <SELECT>
    <SELECT_LIST>
      <SELECT_LIST_ITEM>
        <COLUMN_REF>
          <SCHEMA>MICHAEL</SCHEMA>
          <TABLE>EMP</TABLE>
          <TABLE_ALIAS>E</TABLE_ALIAS>
          <COLUMN_ALIAS>DEPTNO</COLUMN_ALIAS>
          <COLUMN>DEPTNO</COLUMN>
        </COLUMN_REF>
        ....
        ....
        ....
</QUERY>

See here: http://forums.oracle.com/forums/thread.jspa?messageID=3693276&#3693276

Now you ‘only’ need to parse this xml block.

Edit1:

Sadly I don’t fully understand the needs of the OP but I hope this can help (It is another way of asking the ‘names’ of the columns of for example query select count(*),max(dummy) from dual):

set serveroutput on

DECLARE
 c       NUMBER;
 d       NUMBER;
 col_cnt PLS_INTEGER;
 f       BOOLEAN;
 rec_tab dbms_sql.desc_tab;
 col_num NUMBER;

PROCEDURE print_rec(rec in dbms_sql.desc_rec) IS
BEGIN
  dbms_output.new_line;
  dbms_output.put_line('col_type = ' || rec.col_type);
  dbms_output.put_line('col_maxlen = ' || rec.col_max_len);
  dbms_output.put_line('col_name = ' || rec.col_name);
  dbms_output.put_line('col_name_len = ' || rec.col_name_len);
  dbms_output.put_line('col_schema_name= ' || rec.col_schema_name);
  dbms_output.put_line('col_schema_name_len= ' || rec.col_schema_name_len);
  dbms_output.put_line('col_precision = ' || rec.col_precision);
  dbms_output.put_line('col_scale = ' || rec.col_scale);
  dbms_output.put('col_null_ok = ');

  IF (rec.col_null_ok) THEN
    dbms_output.put_line('True');
  ELSE
    dbms_output.put_line('False');
  END IF;
END;

BEGIN
  c := dbms_sql.open_cursor; 
  dbms_sql.parse(c,'select count(*),max(dummy) from dual ',dbms_sql.NATIVE); 
  dbms_sql.describe_columns(c, col_cnt, rec_tab);

  for i in rec_tab.first..rec_tab.last loop
    print_rec(rec_tab(i));
  end loop;

  dbms_sql.close_cursor(c);
END;
/

(See here for more info: http://www.psoug.org/reference/dbms_sql.html)

The OP also want to be able to change the schema name of the table in a query. I think the easiest say to achieve that is to query the table names from user_tables and search in sql statement for those table names and prefix them or to do a 'alter session set current_schema = ....'.