How to get the metadata (in xml format) of all the fileds in SQl query ?

Question

Good day ,
I am using the dbms_xmlgen.getXMLfunction to get the result of any query in xml format.
With this XML I also want the metadata information about all the fields used in the query (passed to getXML function). Is it possible and how can I achieve this.
I tried to Google it but couldn't find any solution , it's easy to do it in java where I can get the resultset meta data from the resultset but I have to do it in Oracle function since I want the result in xml format and want to use the oracle XML API.
You may think why I need metadata , the reason is the application will later use this information to sort the data contained in these fields according to their data type provided to.
Regards
Sajjad Ahmed Paracha

Answer 1

Hi,
Please always say which version of Oracle you're using (SELECT * FROM v$version).
With this XML I also want the metadata information about all the fields used in the query (passed to getXML function). Is it possible and how can I achieve this.It is possible but with a bit of effort.
I would use DBMS_SQL utility to parse the query, extract each column's description and then build a METADATA element with the required information.
Here's an example (11g) :
DECLARE
  v_query      varchar2(30) := 'select * from scott.emp';
  v_cur        integer;
  v_desc_tab   dbms_sql.desc_tab;
  v_col_cnt    number;
  v_col_lst    varchar2(4000);
  v_xml_query  varchar2(32767);
  xml_metadata_coll xmlsequencetype := xmlsequencetype();
  xml_metadata      xmltype;
  res          clob;
BEGIN
  v_cur := dbms_sql.open_cursor;
  dbms_sql.parse(v_cur, v_query, dbms_sql.native);
  dbms_sql.describe_columns(v_cur, v_col_cnt, v_desc_tab);
  dbms_sql.close_cursor(v_cur);
  for i in 1 .. v_col_cnt loop
    if i > 1 then
      v_col_lst := v_col_lst || ', ';
    end if;
    v_col_lst := v_col_lst || v_desc_tab(i).col_name;
    xml_metadata_coll.extend;
    select xmlelement("COLUMN"
           , xmlattributes(v_desc_tab(i).col_name as "name")
           , xmlforest(
               case v_desc_tab(i).col_type
                 when 1   then 'VARCHAR2'
                 when 2   then 'NUMBER'
                 when 12  then 'DATE'
                 when 180 then 'TIMESTAMP'
                 else 'UNKNOWN'
               end as "DATATYPE"
             , v_desc_tab(i).col_max_len as "MAX_LENGTH"
             , v_desc_tab(i).col_precision as "PRECISION"
             , v_desc_tab(i).col_scale as "SCALE"
    into xml_metadata_coll(i)
    from dual;
  end loop;
  v_xml_query :=
'SELECT XMLSerialize(document
         XMLElement("ROOT"
         , :1
         , XMLElement("ROWSET"
           , XMLAgg(
               XMLElement("ROW", XMLForest(' || v_col_lst || '))
         ) as clob indent
FROM ( ' || v_query || ')';
  select xmlelement("METADATA", xmlagg(column_value))
  into xml_metadata
  from table(xml_metadata_coll)
  execute immediate v_xml_query into res using xml_metadata;
  dbms_output.put_line(res);
END;
/Ouput :
<ROOT>
  <METADATA>
    <COLUMN name="EMPNO">
      <DATATYPE>NUMBER</DATATYPE>
      <MAX_LENGTH>22</MAX_LENGTH>
      <PRECISION>4</PRECISION>
      <SCALE>0</SCALE>
    </COLUMN>
    <COLUMN name="ENAME">
      <DATATYPE>VARCHAR2</DATATYPE>
      <MAX_LENGTH>10</MAX_LENGTH>
      <PRECISION>0</PRECISION>
      <SCALE>0</SCALE>
    </COLUMN>
    <COLUMN name="JOB">
      <DATATYPE>VARCHAR2</DATATYPE>
      <MAX_LENGTH>9</MAX_LENGTH>
      <PRECISION>0</PRECISION>
      <SCALE>0</SCALE>
    </COLUMN>
    <COLUMN name="MGR">
      <DATATYPE>NUMBER</DATATYPE>
      <MAX_LENGTH>22</MAX_LENGTH>
      <PRECISION>4</PRECISION>
      <SCALE>0</SCALE>
    </COLUMN>
    <COLUMN name="HIREDATE">
      <DATATYPE>DATE</DATATYPE>
      <MAX_LENGTH>7</MAX_LENGTH>
      <PRECISION>0</PRECISION>
      <SCALE>0</SCALE>
    </COLUMN>
    <COLUMN name="SAL">
      <DATATYPE>NUMBER</DATATYPE>
      <MAX_LENGTH>22</MAX_LENGTH>
      <PRECISION>7</PRECISION>
      <SCALE>2</SCALE>
    </COLUMN>
    <COLUMN name="COMM">
      <DATATYPE>NUMBER</DATATYPE>
      <MAX_LENGTH>22</MAX_LENGTH>
      <PRECISION>7</PRECISION>
      <SCALE>2</SCALE>
    </COLUMN>
    <COLUMN name="DEPTNO">
      <DATATYPE>NUMBER</DATATYPE>
      <MAX_LENGTH>22</MAX_LENGTH>
      <PRECISION>2</PRECISION>
      <SCALE>0</SCALE>
    </COLUMN>
  </METADATA>
  <ROWSET>
    <ROW>
      <EMPNO>7369</EMPNO>
      <ENAME>SMITH</ENAME>
      <JOB>CLERK</JOB>
      <MGR>7902</MGR>
      <HIREDATE>1980-12-17</HIREDATE>
      <SAL>800</SAL>
      <DEPTNO>20</DEPTNO>
    </ROW>
    <ROW>
      <EMPNO>7499</EMPNO>
      <ENAME>ALLEN</ENAME>
      <JOB>SALESMAN</JOB>
      <MGR>7698</MGR>
      <HIREDATE>1981-02-20</HIREDATE>
      <SAL>1600</SAL>
      <COMM>300</COMM>
      <DEPTNO>30</DEPTNO>
    </ROW>
    <ROW>
      <EMPNO>7521</EMPNO>
      <ENAME>WARD</ENAME>
      <JOB>SALESMAN</JOB>
      <MGR>7698</MGR>
      <HIREDATE>1981-02-22</HIREDATE>
      <SAL>1250</SAL>
      <COMM>500</COMM>
      <DEPTNO>30</DEPTNO>
    </ROW>
    <ROW>
      <EMPNO>7566</EMPNO>
      <ENAME>JONES</ENAME>
      <JOB>MANAGER</JOB>
      <MGR>7839</MGR>
      <HIREDATE>1981-04-02</HIREDATE>
      <SAL>2975</SAL>
      <DEPTNO>20</DEPTNO>
    </ROW>
    <ROW>
      <EMPNO>7654</EMPNO>
      <ENAME>MARTIN</ENAME>
      <JOB>SALESMAN</JOB>
      <MGR>7698</MGR>
      <HIREDATE>1981-09-28</HIREDATE>
      <SAL>1250</SAL>
      <COMM>1400</COMM>
      <DEPTNO>30</DEPTNO>
    </ROW>
    <ROW>
      <EMPNO>7698</EMPNO>
      <ENAME>BLAKE</ENAME>
      <JOB>MANAGER</JOB>
      <MGR>7839</MGR>
      <HIREDATE>1981-05-01</HIREDATE>
      <SAL>2850</SAL>
      <DEPTNO>30</DEPTNO>
    </ROW>
    <ROW>
      <EMPNO>7782</EMPNO>
      <ENAME>CLARK</ENAME>
      <JOB>MANAGER</JOB>
      <MGR>7839</MGR>
      <HIREDATE>1981-06-09</HIREDATE>
      <SAL>2450</SAL>
      <DEPTNO>10</DEPTNO>
    </ROW>
    <ROW>
      <EMPNO>7839</EMPNO>
      <ENAME>KING</ENAME>
      <JOB>PRESIDENT</JOB>
      <HIREDATE>1981-11-17</HIREDATE>
      <SAL>5000</SAL>
      <DEPTNO>10</DEPTNO>
    </ROW>
    <ROW>
      <EMPNO>7844</EMPNO>
      <ENAME>TURNER</ENAME>
      <JOB>SALESMAN</JOB>
      <MGR>7698</MGR>
      <HIREDATE>1981-09-08</HIREDATE>
      <SAL>1500</SAL>
      <COMM>0</COMM>
      <DEPTNO>30</DEPTNO>
    </ROW>
    <ROW>
      <EMPNO>7900</EMPNO>
      <ENAME>JAMES</ENAME>
      <JOB>CLERK</JOB>
      <MGR>7698</MGR>
      <HIREDATE>1981-12-03</HIREDATE>
      <SAL>950</SAL>
      <DEPTNO>30</DEPTNO>
    </ROW>
    <ROW>
      <EMPNO>7902</EMPNO>
      <ENAME>FORD</ENAME>
      <JOB>ANALYST</JOB>
      <MGR>7566</MGR>
      <HIREDATE>1981-12-03</HIREDATE>
      <SAL>3000</SAL>
      <DEPTNO>20</DEPTNO>
    </ROW>
    <ROW>
      <EMPNO>7934</EMPNO>
      <ENAME>MILLER</ENAME>
      <JOB>CLERK</JOB>
      <MGR>7782</MGR>
      <HIREDATE>1982-01-23</HIREDATE>
      <SAL>1300</SAL>
      <DEPTNO>10</DEPTNO>
    </ROW>
  </ROWSET>
</ROOT>A couple of comments :
<li> I handle only four datatypes here (VARCHAR2, NUMBER, DATE, TIMESTAMP). Of course you can add more.
The list of Oracle Type Number is available here : http://docs.oracle.com/cd/E11882_01/server.112/e26088/sql_elements001.htm#i54330
Starting with 11g (not sure which release), DBMS_SQL package also declares these numbers through named constants.
<li> I don't use DBMS_XMLGEN in this example. Instead I rebuild the query using SQL/XML functions and the list of columns that's just been described.