How to verify if two tables have exactly the same data?

Question

Basically, we have one table (original table) and it is backed up into another table (backup table); thus the two tables have exactly the same sche

Answer 1

1: First get count for both the tables C1 and C2. C1 and C2 should be equal. C1 and C2 can be obtained from the following query

 select count(*) from table1

if C1 and C2 are not equal, then the tables are not identical.

2: Find distinct count for both the tables DC1 and DC2. DC1 and DC2 should be equal. Number of distinct records can be found using the following query:

select count(*) from (select distinct * from table1)

if DC1 and DC2 are not equal, the tables are not identical.

3: Now get the number of records obtained by performing a union on the 2 tables. Let it be U. Use the following query to get the number of records in a union of 2 tables:

 SELECT count (*)
 FROM 
    (SELECT *
    FROM table1
    UNION
    SELECT *
    FROM table2)

You can say that the data in the 2 tables is identical if distinct count for the 2 tables is equal to the number of records obtained by performing union of the 2 tables. ie DC1 = U and DC2 = U

Answer 2

SELECT * FROM Table1
UNION
SELECT * FROM Table2

If you get records greater than any of two tables, they don't have same data.

Answer 3

You can just use CHECKSUM TABLE and compare the results. You can even alter the table to enable live checksums so that they are continuously available.

CHECKSUM TABLE original_table, backup_table;

It doesn't require the tables to have a primary key.

Answer 4

For the lazier or more SQL-averse developer working with MS SQL Server, I would recommend SQL Delta (www.sqldelta.com) for this and any other database-diff type work. It has a great GUI, is quick and accurate and can diff all database objects, generate and run the necessary change scripts, synchronise entire databases. Its the next best thing to a DBA ;-)

I think there is a similar tool available from RedGate called SQL Compare. I believe some editions of the latest version of Visual Studio (2010) also include a very similar tool.

Answer 5

Please try the following method for determining if two tables are exactly the same, when there is no primary key of any kind and there are no duplicate rows within a table, using the below logic:

Step 1 - Test for Duplicate Rows on TABLEA

If SELECT DISTINCT * FROM TABLEA

has the same row count as

SELECT * FROM TABLEA

then go to the next step, otherwise you can't use this method...

Step 2 - Test for Duplicate Rows on TABLEB

If SELECT DISTINCT * FROM TABLEB

has the same row count as

SELECT * FROM TABLEB

then go to the next step, else you can't use this method...

Step 3 - INNER JOIN TABLEA to TABLEB on every column

If the row count of the below query has the same row count as the row counts from Steps 1 and 2, then the tables are the same:

SELECT
*

FROM
TABLEA

INNER JOIN TABLEA ON
TABLEA.column1 = TABLEB.column1
AND TABLEA.column2 = TABLEB.column2
AND TABLEA.column3 = TABLEB.column3 
--etc...for every column

Note that this method doesn't necessarily test for different data types, and probably won't work on non-joinable data types (like VARBINARY)

Feedback welcome!

Answer 6

select count(*) 
from lemmas as original_table 
      full join backup_table using (lemma_id)
where backup_table.lemma_id is null
      or original_table.lemma_id is null
      or original_table.lemma != backup_table.lemma

The full join / check for null should cover additions or deletions as well as changes.

• backup.id is null = addition
• original.id is null = deletion
• neither null = change