By: Harry Dragstra

Harry Dragstra — Fri, 06 Jul 2012 09:26:16 +0000

Well, you better forget about my last comment… the ORA_HASH function, used in the way I do, isn’t consistent in the result value.
And if result values differ in time for identical input, comparing two tables that use this function will (almost ) always result in 1 ( tables differ ).
See for more info about the ORA_HASH function:
http://jonathanlewis.wordpress.com/2009/11/21/ora_hash-function/

By: Harry Dragstra

Harry Dragstra — Fri, 06 Jul 2012 07:49:47 +0000

I discovered that there is an easy ( without using dbms_lob.compare ) full proof solution, by applying the ORA_HASH function ( available as of 10g Release 1 ). The docs - http://docs.oracle.com/cd/B13789_01/server.101/b10759/functions097.htm - mentione explicitly that there is "no restrictions on the type or length of data", so I tested it on LONG's too. And indeed... no problem at all. Here is the the changed code, using the ORA_HASH function now:


SQL> set linesize 300 pagesize 0 heading off    
SQL> select text from user_source where type='FUNCTION' and name ='DIFF_TABLES' order by line;
FUNCTION Diff_Tables
    ( P_name_tab1   VARCHAR2
    , P_name_tab2   VARCHAR2
    , P_owner_tab1  VARCHAR2 := USER
    , P_owner_tab2  VARCHAR2 := USER )
  RETURN PLS_INTEGER
IS

  v_tab1   VARCHAR2(100)  := UPPER(TRIM(P_owner_tab1||'.'||P_name_tab1));
  v_tab2   VARCHAR2(100)  := UPPER(TRIM(P_owner_tab2||'.'||P_name_tab2));
  v_clist  VARCHAR2(4000) := NULL;
  v_col    VARCHAR2(100);
  cntr     PLS_INTEGER := 0;
  cnt1     NUMBER := 0;
  cnt2     NUMBER := 0;
  v_ret    PLS_INTEGER := 0;

BEGIN

-- setup the column list
  for x in ( select column_name
                  , data_type
             from dba_tab_columns
             where owner||'.'||table_name = v_tab1
             order by column_id )
  loop
    cntr := cntr + 1;
    if x.data_type in ('CLOB','BLOB','LONG') then
      v_col := 'ORA_HASH('||x.column_name||')';
--      v_col := 'DBMS_LOB.SUBSTR('||x.column_name||',2000), DBMS_LOB.GETLENGTH('||x.column_name||')';
    else
      v_col := x.column_name;
    end if;
    if cntr != 1 then
      v_col := ','||v_col;
    end if;
    v_clist := v_clist||v_col;
  end loop;

-- compare
  EXECUTE IMMEDIATE 'select count(*) from ( select '||v_clist||' from '||v_tab1||' minus select '||v_clist||' from '||v_tab2||' )' INTO cnt1;
  EXECUTE IMMEDIATE 'select count(*) from ( select '||v_clist||' from '||v_tab2||' minus select '||v_clist||' from '||v_tab1||' )' INTO cnt2;

-- return 0 if tables match, and 1 if tables differ.
  if (cnt1+cnt2) > 0 then
    v_ret := 1;
  end if;

  return v_ret;

END Diff_Tables;

50 rows selected.

SQL>

Comments on: Compare tables with the minus operator, even if they contain clobs and/or blobs.

By: Harry Dragstra

By: Harry Dragstra