Select data from all tables which contain these data-column - oracle

Question

( I think it could be a simple question for the most users here ..)
Short description:
I need a way (maybe with PL/SQL which I don't know ..) to "select defined data from all tables which contain this type of data"
Long description (example):
I have a different number of different tables. An often changing part of them - I don't know the number and the names - contains the column "FID". Now I need two steps:
a) Select all tables which contain the column "FID". ( I know how to do this as single step)
b) Select from all found tables the value FID and show it.
For me the problem is the step from a) to b). With known tables I would use UNION, but with a dynamic result of tables I have no idea ..

Answer 1

You could use a variation on an XML magic trick, by using dbms_xmlgen to get all the values into XML documents based on a query against user_tab_columns:
select dbms_xmlgen.getxmltype(
'select "' || column_name || '" from "' || table_name || '"')
from user_tab_columns
where upper(column_name) = 'FID'
and data_type = 'NUMBER';
... where I'm assuming FID is expected to be a numeric ID, so limiting only to numeric columns (and also allowing for mixed case/quoted identifiers for table and columns names, just in case). That gives one row per table, with an XML document listing the FID values in that table.
Then from that XML you can extract the individual values, again as numbers:
with cte (xml) as (
select dbms_xmlgen.getxmltype(
'select "' || column_name || '" as fid from "' || table_name || '"')
from user_tab_columns
where upper(column_name) = 'FID'
and data_type = 'NUMBER'
)
select x.fid
from cte
cross apply xmltable(
'/ROWSET/ROW'
passing cte.xml
columns fid number path 'FID'
) x;
Or if you want to see the table/column each value came from, just include those in the CTE and select list:
with cte (table_name, column_name, xml) as (
select table_name, column_name, dbms_xmlgen.getxmltype(
'select "' || column_name || '" as fid from "' || table_name || '"')
from user_tab_columns
where upper(column_name) = 'FID'
and data_type = 'NUMBER'
)
select cte.table_name, cte.column_name, x.fid
from cte
cross apply xmltable(
'/ROWSET/ROW'
passing cte.xml
columns fid number path 'FID'
) x;
If you want to search other schemas, then use all_tab_columns instead, and optionally include each table's owner:
with cte (owner, table_name, column_name, xml) as (
select owner, table_name, column_name, dbms_xmlgen.getxmltype(
'select "' || column_name || '" as fid from "' || owner || '"."' || table_name || '"')
from all_tab_columns
where upper(column_name) = 'FID'
and data_type = 'NUMBER'
)
select cte.owner, cte.table_name, cte.column_name, x.fid
from cte
cross apply xmltable(
'/ROWSET/ROW'
passing cte.xml
columns fid number path 'FID'
) x;
db<>fiddle
The basis for this trick goes back to at least 2007 but may be even older, from before getxmltype() existed (it seems to have been added in 10g); I'd originally used xmltype(getxml()):
select xmltype(dbms_xmlgen.getxml(
'select "' || column_name || '" from "' || table_name || '"'))
from user_tab_columns
where upper(column_name) = 'FID'
and data_type = 'NUMBER';
which works most of the time, but if any of the tables are empty throws "ORA-06502: PL/SQL: numeric or value error".

Answer 2

If you want to use pl/sql I really love pipelined functions:
create type result_type as Object ( text varchar2(2000) );
create type result_type_table as table of result_type;
create or replace function select_all( p_column_name in varchar2 )
return result_type_table
deterministic
pipelined
as
v_table_name varchar2(40);
v_result result_type := result_type('');
v_table_name_cursor sys_refcursor;
v_inner_cursor sys_refcursor;
begin
open v_table_name_cursor
for 'select a.table_name
from user_tab_cols a
, user_tables b
where a.column_name = :1
and a.table_name = b.table_name'
using upper(p_column_name);
loop
fetch v_table_name_cursor into v_table_name;
exit when v_table_name_cursor%notfound;
open v_inner_cursor
for 'select '||p_column_name||' from '||v_table_name;
loop
fetch v_inner_cursor into v_result.text;
exit when v_inner_cursor%notfound;
pipe row (v_result );
end loop;
close v_inner_cursor;
end loop;
close v_table_name_cursor;
end;
/
Using this function is simple:
select * from table( select_all('your_column_name') );
db<>fiddle