Go Premium for a chance to win a PS4. Enter to Win

x
?
Solved

Best way to compare Data in tables

Posted on 2011-09-14
7
Medium Priority
?
216 Views
Last Modified: 2013-12-17
Hi Experts.

I need to compare Data in a table with new information downloaded from a server.

This means the follwoing:

1. I download data from the webserver.
2. Read the data.
3. Before inserting, compare first. If the data is equal, then skip, if there is a change, then update and store the old value in a different table.

I have about 90 Columns in each table, this means that i dont want to make 90 if else statements.

I am using Linq To SQL

I need a way to do this dynamically.

Best Regards,

John Johnson.
0
Comment
Question by:databoks
  • 3
  • 2
  • 2
7 Comments
 
LVL 43

Expert Comment

by:Eugene Z
ID: 36535324
what is your sql server version/edition/sp?

try to use EXISTS
http://msdn.microsoft.com/en-us/library/ms188336.aspx

if you are in sqlserver 2005 and up
try EXCEPT
http://msdn.microsoft.com/en-us/library/ms188055.aspx
0
 
LVL 4

Expert Comment

by:rbride
ID: 36535536
Step 3 is the biggie here.

3. Before inserting, compare first. If the data is equal, then skip, if there is a change, then update and store the old value in a different table.

OK So I am assuming that you have the ability to identify your incoming data, i.e. you have some kind of a key. If that is the case then you can simply use the CHECKSUM function.

drop table t
go
drop table t2
go

create table t
(i int, v varchar(10), v2 varchar(10))
go
insert t values (1, 'abc', 'xyz')
insert t values (2, 'abcd', 'ghi')
go

create table t2 (i int, v varchar(10), v2 varchar(10), )
go

insert t2 values (1, 'abc', 'xyz')
insert t2 values (2, 'abd', 'ghi')
insert t2 values (3, 'edcd', 'xx')
go

ALTER TABLE t ADD CHK AS CHECKSUM(v,v2)
go
ALTER TABLE t2 ADD CHK AS CHECKSUM(v,v2)
go

select *
from t join t2 on t.i = t2.i
where t.chk <> t2.chk
go

However see [http://msdn.microsoft.com/en-us/library/ms189788.aspx]
If one of the values in the expression list changes, the checksum of the list also generally changes. However, there is a small chance that the checksum will not change

The other way to do it is to create the comparison statement using dynamic sql. First of all you need to build you query by getting meta information about your columns. For nullable columns, you can't just check with not equals, thus it is a little bit complicated:

select
'(' +
CASE
WHEN IS_NULLABLE = 'YES'
THEN '(t1.' + COLUMN_NAME + ' IS NULL AND t2.' + COLUMN_NAME + ' IS NOT NULL)'
     + ' OR ' +
     '(t2.' + COLUMN_NAME + ' IS NULL AND t1.' + COLUMN_NAME + ' IS NOT NULL)'
     + ' OR '
ELSE ''
END + '(t1.' + COLUMN_NAME + ' <> ' + 't2.' + COLUMN_NAME + ')'
from INFORMATION_SCHEMA.COLUMNS
where TABLE_NAME = 't'


This will produce a list like this which you have to build together into a string. Write a loop and build up your query that way.

((t1.i IS NULL AND t2.i IS NOT NULL) OR (t2.i IS NULL AND t1.i IS NOT NULL) OR (t1.i <> t2.i)
((t1.v IS NULL AND t2.v IS NOT NULL) OR (t2.v IS NULL AND t1.v IS NOT NULL) OR (t1.v <> t2.v)
((t1.v2 IS NULL AND t2.v2 IS NOT NULL) OR (t2.v2 IS NULL AND t1.v2 IS NOT NULL) OR (t1.v2 <> t2.v2)
0
 
LVL 4

Expert Comment

by:rbride
ID: 36535571
Um I forgot to add:
of course, if your table structure is static, just use the dynamic SQL above and
edit it all together as:

--> run this
select
CASE
WHEN IS_NULLABLE = 'YES'
THEN '(t1.' + COLUMN_NAME + ' IS NULL AND t2.' + COLUMN_NAME + ' IS NOT NULL)'
     + ' OR ' +
     '(t2.' + COLUMN_NAME + ' IS NULL AND t1.' + COLUMN_NAME + ' IS NOT NULL)'
     + ' OR '
ELSE ''
END + '(t1.' + COLUMN_NAME + ' <> ' + 't2.' + COLUMN_NAME + ') OR'
from INFORMATION_SCHEMA.COLUMNS
where TABLE_NAME = 't'

Copy the results put together something like this:

select t2.*
from t as t1 join t2 as t2 on t1.i = t2.i
where
(t1.v IS NULL AND t2.v IS NOT NULL) OR (t2.v IS NULL AND t1.v IS NOT NULL) OR (t1.v <> t2.v) OR
(t1.v2 IS NULL AND t2.v2 IS NOT NULL) OR (t2.v2 IS NULL AND t1.v2 IS NOT NULL) OR (t1.v2 <> t2.v2)

And that is your final statement to run. Of course you can always do this on the fly using the exec function but you need to program a lot more around it to get everything working.
0
What does it mean to be "Always On"?

Is your cloud always on? With an Always On cloud you won't have to worry about downtime for maintenance or software application code updates, ensuring that your bottom line isn't affected.

 
LVL 8

Author Comment

by:databoks
ID: 36536396
Thanks guy.

I forgot to mention that i download a XML file containig the data. I search through the XML for changes..

I use c#. I need c# code if possible.
0
 
LVL 43

Expert Comment

by:Eugene Z
ID: 36538118
OK
CHECK
compare 2 xml files with csharp

http://www.daniweb.com/software-development/csharp/threads/46345
0
 
LVL 8

Accepted Solution

by:
databoks earned 0 total points
ID: 36945511
I did this by using if else statements..
0
 
LVL 8

Author Closing Comment

by:databoks
ID: 36972733
i fixed this by using if else statements.
0

Featured Post

Independent Software Vendors: We Want Your Opinion

We value your feedback.

Take our survey and automatically be enter to win anyone of the following:
Yeti Cooler, Amazon eGift Card, and Movie eGift Card!

Question has a verified solution.

If you are experiencing a similar issue, please ask a related question

In part one, we reviewed the prerequisites required for installing SQL Server vNext. In this part we will explore how to install Microsoft's SQL Server on Ubuntu 16.04.
Microsoft Access has a limit of 255 columns in a single table; SQL Server allows tables with over 255 columns, but reading that data is not necessarily simple.  The final solution for this task involved creating a custom text parser and then reading…
Via a live example combined with referencing Books Online, show some of the information that can be extracted from the Catalog Views in SQL Server.
Viewers will learn how to use the INSERT statement to insert data into their tables. It will also introduce the NULL statement, to show them what happens when no value is giving for any given column.

916 members asked questions and received personalized solutions in the past 7 days.

Join the community of 500,000 technology professionals and ask your questions.

Join & Ask a Question