Oracle how to address column in PL/SQL FOR LOOP by it's position instead of column name - oracle

Question

Is there a way to address column by it's position in PL/SQL, something like this
BEGIN
FOR r IN (SELECT * FROM table)
LOOP
DBMS_OUTPUT.PUT_LINE(r.(1));
END LOOP;
END;
I tried both bracket types but always get
PLS-00103: Encountered the symbol "(" when expecting one of the following
I also tried BULK COLECT INTO with table of varray but then I get
PLS-00642: local collection types not allowed in SQL statements
And if I declare table with %ROWTYPE and bulk it then it seems to behave the same way as the normal loop.
I tried to look into documentation but couldn't find any example of this scenario.

Answer 1

Using the DBMS_SQL package and the COLUMN_VALUE procedure: but that's a lot of work... probably overkilling for your actual needs: you have to open a sys_refcursor for the query, convert it into a cursor number with DBMS_SQL.TO_CURSOR_NUMBER, collect the descriptions of the columns with DBMS_SQL.DESCRIBE_COLUMNS and loop on the column count and fetch the value with DBMS_SQL.COLUMN_VALUE into a specific variable according to its type...

Answer 2

In general, no. Oracle does not support accessing records by position; only by identifier.
You can approach the problem slightly differently and, instead of using SELECT *, you can explicitly list the columns to select and give them numeric column aliases:
BEGIN
FOR r IN (SELECT dummy AS "1" FROM DUAL)
LOOP
DBMS_OUTPUT.PUT_LINE(r."1");
END LOOP;
END;
/
You are still referring to the columns by name; only now their names are the "numeric" aliases.
Note: Personally, I would stick to using the column names and not try to find work-arounds to use positions as positions can change if columns are deleted from the table.

Answer 3

If you want to have a matrix in PL/SQL you could define one as an indexed table of an indexed table of whatever data type you're dealing with, something like:
type t_row is table of varchar2(1) index by pls_integer;
type t_tab is table of t_row index by pls_integer;
l_matrix t_tab;
The tricky part is populating it. DBMS_SQL is certainly one approach, but partly for fun, you could use XML. The DBMS_XMLGEN package lets you run a query and get the results back as an XML document with a ROWSET root node. You can then count the ROW nodes under that, and assuming there are any, count the nodes within the first ROW - which gives the matrix dimensions.
You can then use nested loops to populate the matrix, and once done, you can refer to an element as for example l_matrix(3)(2).
This is a working example, where the table being queried has values that are all a single character, for simplicity; you would need to change the matrix definition to handle the data you expect.
DECLARE
-- elements of matrix need to be data type and size suitable for your data
type t_row is table of varchar2(1) index by pls_integer;
type t_tab is table of t_row index by pls_integer;
l_matrix t_tab;
l_xml xmltype;
l_rows pls_integer;
l_cols pls_integer;
BEGIN
l_xml := dbms_xmlgen.getxmltype('SELECT * FROM your_table');
SELECT XMLQuery('count(/ROWSET/ROW)'
PASSING l_xml
RETURNING CONTENT).getnumberval()
INTO l_rows
FROM DUAL;
IF l_rows = 0 THEN
dbms_output.put_line('No data');
RETURN;
END IF;
SELECT XMLQuery('count(/ROWSET/ROW[1]/*)'
PASSING l_xml
RETURNING CONTENT).getnumberval()
INTO l_cols
FROM DUAL;
dbms_output.put_line('Rows: ' || l_rows || ' Cols: ' || l_cols);
-- populate matrix
FOR i IN 1..l_rows LOOP
FOR j in 1..l_cols LOOP
l_matrix(i)(j) := l_xml.extract('/ROWSET/ROW[' || i || ']/*[' || j || ']/text()').getstringval();
END LOOP;
END LOOP;
-- refer to a specific element
dbms_output.put_line('Element 3,2 should be H; is actually: ' || l_matrix(3)(2));
-- display all elements as list
FOR i IN 1..l_matrix.COUNT LOOP
FOR j IN 1..l_matrix(i).COUNT LOOP
dbms_output.put_line('Row ' || i || ' col ' || j || ': ' || l_matrix(i)(j));
END LOOP;
END LOOP;
-- display all elements as grid
FOR i IN 1..l_matrix.COUNT LOOP
FOR j IN 1..l_matrix(i).COUNT LOOP
IF j > 0 THEN
dbms_output.put(' ');
END IF;
-- format/pad real data to align it; simple here with single-char values
dbms_output.put(l_matrix(i)(j));
END LOOP;
dbms_output.new_line;
END LOOP;
END;
/
With my sample table that outputs:
Rows: 4 Cols: 3
Element 3,2 should be H; is actually: H
Row 1 col 1: A
Row 1 col 2: B
Row 1 col 3: C
Row 2 col 1: D
Row 2 col 2: E
Row 2 col 3: F
Row 3 col 1: G
Row 3 col 2: H
Row 3 col 3: I
Row 4 col 1: J
Row 4 col 2: K
Row 4 col 3: L
A B C
D E F
G H I
J K L
fiddle
As #astenx said in a comment, you can use JSON instead of XML; which would allow you to populate the matrix like this.
That has raised something else I'd overlooked. My dummy table doesn't have an ID column or an obvious way of ordering the results. For the JSON version I used rownum, but in both that and the original query the order of the rows (in the result set, and thus in the matrix) is currently indeterminate. You need to have a column you can order by in the query, or some other way to determine the sequence of rows.