Oracle比较两个不同表之间的数据

Question

I have two table one is having all field VARCHAR2 but other having different type for different data.

For Example :

Table One
==========================
Col 1           VARCHAR2  UNIQUE KEY
Col 2           VARCHAR2
Col 3           VARCHAR2
===========================

Table Two
==========================
Col One         VARCHAR2  UNIQUE KEY
Col Two         TIMESTAMP
Col Three       NUMBER
==========================

we are having one mapping table. it denotes which column of Table One has to compare with which column of Table Two. For Example

Mapping Table
==============================
Table One           Table Two
==============================

Col 1               Col One
Col 2               Col Three
Col 3               Col Two
==============================

Now with the help of UNIQUE KEY of TABLE ONE we have to find same row in TABLE TWO and compare rows column by column and get changes in data. Currently we are using java program for comparing data row by row and column by column and getting changes between data in rows with same UNIQUE KEY. it is working fine but taking too much time as we are having 100000 records in DB.

Now my question is : is there any way i can compare data at SQL level and get changes in data?

Answer 1

You can do it 'manually' with a query like this: It's a lot of work, but there are only three different types of checks you need to do, so it's not very complex:

select
  *
from
  Table1 t1
  full outer join Table2 t2 on t2.ID = t1.ID
where
  -- Check ID, either record does not exist in either table.
  t1.ID is null or 
  t2.ID = null or
  -- Not nullable field can be easily compared.
  t1.NotNullableField1 <> t2.NotNUllableField1 or
  -- Nullable field is slightly more work.
  t1.NullableField1 <> t2.NullableField1 or
  (t1.NullableField1 is null and t2.NullableField1 is not null) or
  (t1.NullableField1 is not null and t2.NullableField1 is null)

Another solution is to use MINUS, which is a bit like UNION, only it returns a dataset minus the records in a second dataset:

select * from Table1 t1
MINUS
select * from Table2 t2

This works only one way (which might be fine for your purpose), but you can also combine it with UNION to make it bidirectional.

select
  *
from
    ( select * from Table1
      MINUS
      select * from Table2)
    UNION ALL
    ( select * from Table2
      MINUS
      select * from Table1)

The output of both solutions is a bit different.

In the FULL OUTER JOIN query, the IDs will be joined and the values of the matching rows will be displayed next to each other as a single row.

In the MINUS query, the result will be presented as a single dataset. If a record does not exist in either one table, it will be displayed. If a record (ID) exists in both tables, but other fields are different, you will get both rows. So it's a bit harder to compare them.

See: http://www.techonthenet.com/oracle/minus.php