How to read the same column from every table in a database? - sql

Question

I have a huge database with 400+ tables. Each table has the same column id for the Primary key and "timestamp_modify" in which the last change of the table is done.
So what I want are 2 things:
Now I want a list of all changes by ID and table name like:
Table | id | timestamp_modiy
Kid | 1 | 24.10.2021 00:01
Parent | 1000 | 24.10.2021 00:02
The only, very bad way I could come up with, is that I make a view in which I include every damn table by hand and read out the values...
Is there a better way?

Answer 1

How about a pipelined function?
Just setting datetime format (you don't have to do that):
SQL> alter session set nls_date_format = 'dd.mm.yyyy hh24:mi:ss';
Session altered.
Types:
SQL> create or replace type t_row as object
2 (table_name varchar2(30),
3 id number,
4 timestamp_modify date)
5 /
Type created.
SQL> create or replace type t_tab is table of t_row;
2 /
Type created.
Function: querying user_tab_columns, its cursor FOR loop fetches tables that contain both ID and TIMESTAMP_MODIFY columns, dynamically creates select statement to return the last (MAX function, to avoid too_many_rows) columns' values for the last TIMESTAMP_MODIFY value (returned by the subquery).
SQL> create or replace function f_test
2 return t_tab pipelined
3 as
4 l_str varchar2(500);
5 l_id number;
6 l_timestamp_modify date;
7 begin
8 for cur_r in (select table_name from user_tab_columns
9 where column_name = 'ID'
10 intersect
11 select table_name from user_tab_columns
12 where column_name = 'TIMESTAMP_MODIFY'
13 )
14 loop
15 l_str := 'select max(a.id) id, max(a.timestamp_modify) timestamp_modify ' ||
16 'from ' || cur_r.table_name || ' a ' ||
17 'where a.timestamp_modify = ' ||
18 ' (select max(b.timestamp_modify) ' ||
19 ' from ' || cur_r.table_name || ' b ' ||
20 ' where b.id = a.id)';
21 execute immediate l_str into l_id, l_timestamp_modify;
22 pipe row(t_row(cur_r.table_name, l_id, l_timestamp_modify));
23 end loop;
24 end;
25 /
Function created.
Testing:
SQL> select * from table(f_test);
TABLE_NAME ID TIMESTAMP_MODIFY
------------------------------ ---------- -------------------
TABA 1 24.10.2021 14:59:29
TAB_1 1 24.10.2021 15:03:16
TAB_2 25 24.10.2021 15:03:36
TEST 5 24.10.2021 15:04:24
SQL>

Answer 2

Yes, the only way is to union all all tables, like:
select id, timestamp_modify
from kid
union all
select id, timestamp_modify
from parent
union all
...
The performance will be awful, since all the tables will be scanned every time :(
I think that you might reconsider you db design...

Answer 3

You can build a procedure for this, but even so it will have some impact in performance. Although there is a loop, with SQL Dynamic, you might only need 400 iterations, and in each one you will insert all the ids of that table.
I am taking some assumptions
You want all the IDs and their corresponding timestamp_modify per table
I create a table to store the results. If you use it with the same name always it will recycle the object. If you not, you can keep a history
I am assuming that only one timestamp_modify row is present per ID
I filter only the tables of your schema that contain both columns.
The table contains also the table_name that you can identify where the record is coming from.
One example
create or replace procedure pr_build_output ( p_tmp_table in varchar2 default 'TMP_RESULT' )
is
vcounter pls_integer;
vsql clob;
vtimestamp date; -- or timestamp
begin
-- create table to store results
select count(*) into vcounter from all_tables where table_name = upper(p_tmp_table) and owner = 'MY_SCHEMA';
if vcounter = 1
then
execute immediate ' drop table '||p_tmp_table||' purge ' ;
end if;
vsql := ' create table '||p_tmp_table||'
( table_name varchar2(128) ,
id number,
timestamp_modify date -- or timestamp
) ';
execute immediate vsql ;
-- Populate rows
for h in
( select a.table_name from all_tables a
where a.owner = 'MY_SCHEMA'
and a.table_name in ( select distinct b.table_name from all_tab_columns b where b.owner = 'MY_SCHEMA'
and b.column_name = 'ID' and b.column_name = 'TIMESTAMP_MODIFY'
)
)
loop
vsql := ' insert into '||p_tmp_table||' ( table_name , id, timestamp_modify )
select '''||h.table_name||''' as table_name , id , timestamp_modify
from my_schema.'||h.table_name||'
' ;
execute immediate vsql ;
commit ;
end loop;
exception when others then raise;
end;
/