Iterate through row's columns - sql

Question

I have table with 100 columns with not correlated names (ABC1, DA23, EE123 - there is no common pattern there).
I want to iterate through every row and every column in this table.
My current script:
BEGIN
FOR single_row IN (
SELECT *
FROM MY_TABLE)
LOOP
--iterate through columns of 'single_row'
--for each nullable column do insert with real current column name and column value)
--I assume each column is nullable except of ID
INSERT INTO ANOTHER_TABLE VALUES (single_row.id, column_name, column_value);
END LOOP;
END;
So for example, if MY_TABLE contains 2 rows:
ID|ABC1|DA23|EE123|...
1|123|456|789|...
2|321|654|987|...
After running my script, my ANOTHER_TABLE will contain:
MY_TABLE_ID|COLUMN_NAME|COLUMN_VALUE
1|ABC1|123
1|DA23|456
1|EE123|789
... other columns from row 1
2|ABC1|321
2|DA23|654
2|EE123|987
... other columns from row 2
How I can do this?
I'm using Oracle 11g
EDIT
#vkp provided great solution, but there is one more thing to solve. I don't want to specify all columns in in clause. I would love to use some kind of query there or * or anything else, just to not be forced to list all of them.
I have tried something like this:
select *
from MY_TABLE t
unpivot (
column_value for column_name in (select column_name
from user_tab_columns
where table_name = 'MY_TABLE'
and nullable = 'Y')
) u
but it returns error:
ORA-00904: : invalid identifier
00904. 00000 - "%s: invalid identifier"

Answer 1

This is an application of unpivot.
select *
from my_table m
unpivot (column_value for column_name in (ABC1,DA23,EE123)) u
null values for any of the columns for an id won't be shown in the result.
If you have to include null values in the output, use the option INCLUDE NULLS.
select *
from my_table m
unpivot include nulls (column_value for column_name in (ABC1,DA23,EE123)) u
Edit: To include column names dynamically, use
DECLARE
sql_stmt VARCHAR2(4000);
var_columns VARCHAR2(4000); --use clob datatype if the column names can't fit in with this datatype
BEGIN
SELECT LISTAGG(column_name,',') WITHIN GROUP(ORDER BY column_name)
INTO var_columns
FROM user_tab_columns
WHERE table_name='MY_TABLE' AND column_name<>'ID';
sql_stmt:='select * from my_table m
unpivot
(column_value for column_name in (' || var_columns || ')) u';
EXECUTE IMMEDIATE sql_stmt;
END;
/

Answer 2

First option. With dynamic sql.
declare
v_ctx number;
v_query varchar2(500);
v_total NUMBER;
v_desctab DBMS_SQL.DESC_TAB;
v_column_cnt NUMBER;
v_value varchar2(32767);
v_result clob := '';
v_rownum number := 0;
begin
v_ctx := dbms_sql.open_cursor;
v_query := 'select * from user_objects where rownum < 100';
dbms_sql.parse(v_ctx,v_query,dbms_sql.v7);
v_total := dbms_sql.execute(v_ctx);
DBMS_SQL.DESCRIBE_COLUMNS(v_ctx, v_column_cnt, v_desctab);
for i in 1 .. v_column_cnt loop
dbms_sql.define_column(v_ctx, i, v_value /* data_type varchar2*/, 32767 /* max_length*/);
end loop;
loop
exit when dbms_sql.fetch_rows(v_ctx) = 0;
v_rownum := v_rownum +1;
for i in 1 .. v_column_cnt loop
dbms_sql.column_value(v_ctx, i, v_value);
dbms_output.put_line(v_rownum||' - '||v_desctab(i).col_name||' - '||v_value);
end loop;
end loop;
dbms_sql.close_cursor(v_ctx);
exception
when others then
dbms_sql.close_cursor(v_ctx);
raise;
end;
/
2nd option with xquery.
select t1.id,t2.* from xmltable('for $i in ora:view("<you_table_here>")/ROW
return $i'
columns id FOR ORDINALITY
, row_value xmltype path'.'
) t1
,xmltable('for $i in $row_value/ROW/* return $i'
passing t1.row_value as "row_value"
columns col_index for ORDINALITY ,
column_name varchar2(100) path 'name()',
column_value varchar2(100) path 'text()'
) t2

Answer 3

Here is a simple solution using REF CURSOR.
I've tried this code and it's working at my end.
DECLARE
query_2 VARCHAR2(1000);
TYPE icur IS REF CURSOR;
ic icur;
col_val VARCHAR2(100);
BEGIN
FOR j IN
(SELECT * FROM user_tab_cols WHERE table_name = UPPER('MY_TABLE'))
LOOP
dbms_output.put_line(j.column_name);
query_2 := 'SELECT ' || j.column_name|| ' FROM MY_TABLE';
OPEN ic FOR query_2;
LOOP
FETCH ic INTO col_val;
EXIT WHEN ic%NOTFOUND;
INSERT INTO ANOTHER_TABLE VALUES( j.column_name, col_val);
END LOOP;
END LOOP;
END;
/