I'm working with a decently large software platform that utilizes Microsoft SQL Server 2008 R2. I'm investigating a very rare bug where something in the database is updating ContactInfo's primary key (CID) to 0. The table has two primary keys. CID is related to a primary key in another table to store contact information.
Is there a way to make an existing update trigger capture what stored procedure is making an update to the table? Or even better, is there a way to capture Profiler data in an audit table, such as stored procedure execution statement with input parameters? We could continuously run a Profiler trace to try to catch the update in real time but the the infrequency of the bug would result in at least a few hundred gigs of trace data to be stored, which is not an option.
Below is my code for the existing audit table. There are 28 columns, so I just replaced them with [columns] for simplicity and space.
ALTER TRIGGER [dbo].[wt_ContactInfo_U]
ON [dbo].[ContactInfo]
FOR UPDATE AS
INSERT INTO [dbo].[ContactInfo_AUDIT] ( // columns )
SELECT // columns
FROM Deleted D
WHERE
CHECKSUM( // D.[columns]) NOT IN (SELECT CHECKSUM( // I.[columns])
FROM INSERTED I
WHERE I.[CID] = D.[CID])
I have a script for microsoft sql server database which has hundreds of tables and tables contains data as well. This is the database of a web application.what I want to do is to delete the previous records and reset the primary key to 1 or 0.
I have tried
`DBCC CHECKIDENT ('dbo.tbl',RESEED,0); `
but it does not work for me as in most of the tables the primary key is not identity.
I can not truncate the table as its primary key is being used as FK in many other tables.
I have also tried to add the identity specification in the primary key of the table and run the checkident query and then changing it back to non-identity spec, but after adding the record again it starts from where it left.
Making changes in the code is not an option for me.
please help.
According with your question I am not sure about the main objective, Why? If you need truncate a lot of tables and change their structures to have an Identity property why you can't disabled the FK? . In the past I have used an standard process for rebuild a table and migrate all the information, this represent a group of steps, I would try to help you but you should follow the next steps.
Steps:
1) Disable FK for alter the structure of your tables. You can get the solution for this task in the next link:
Temporarily disable all foreign key constraints
2) Alter the table with the new property Identity, this is a classic process of ALTER TABLE xxxxxx.
3) Execute the syntax that previously posted :
DBCC CHECKIDENT ('dbo.tbl',RESEED,0);
Try to follow this path and if you have any problem only ask us.
You can not truncate table that have relation. You shoud remove relation firstly.
My understanding of this question:
You have a database with tables that you want to empty and next have them use primary key values starting at 0 or 1.
Some of these tables use an identity value and you already have a solution for those (you know you can find out which columns have an identity by using the sys.columns view? Look for the is_identity column).
Some tables do not use an identity but get their pk values from an unknown source, which we can't modify.
The only solution I see, is creating an after insert trigger (or modifying) on those tables that subtracts from the new pk value.
E.g.: your "hidden generator" will generate a next value 5254, but you want the next pk value to become one:
CREATE TRIGGER trg_sometable_ai
ON sometable
AFTER INSERT
AS
BEGIN
UPDATE st
SET st.pk_col = st.pk_col - 5253
FROM sometable AS st
INNER JOIN INSERTED AS i
ON i.pk_col = th.pk_col
END
You'll have to determine the next value and thus the "subtract value" for each table.
If the code also inserts child records into tables with a foreign key to this table, and uses the previously generated value, you have to modify those triggers as well...
This is a "last resort" solution and something I would recommend against in any scenario that has other options. Manipulating primary key values is generally not a good idea.
I am using SQL Azure. I have a deployment DB and a test DB
I would like to add some new lookup records to the Test DB, to test new code.
Initially My Deployment DB's Identity was set to 200000+ for the PKs, and my Test DB to 100000+, to prevent PK collisions when syncing using such tools as Redgates' SQL data compare.
Unfortunately I made a mistake, and copied the Deployment DB as the new Test DB, since we required a more up to date dataset. As a result my Test DB now starts at 200000+. So I now have the risk of conflicts when syncing with the Deployment DB.
I would normallly just use:
DBCC CHECKIDENT('TableName', RESEED, 105000)
However SQL Azure does not support this.
I have come across a workaround:
set identity_insert TableName on -- this basically turns off IDENTITY
INSERT INTO TableName(id, name) VALUES (104999,'Test Reset Identity Start 104999') -- so we can jam any value for column ID
set identity_insert TableName off -- then turn it back on
INSERT INTO TableName(name) VALUES ('Test Reset Identity End') -- ID starts at 105000, in theory, from this point
SELECT * FROM TableName
However the new Identify value always seems to take the highest PK in the table as the last seed, rather than the PK value from the last inserted record.
I would rather not rebuild the table.
Is there another approach to resetting the identity value for my situation, ie to a lesser number ie 104999 rather the current 204999?
Thanks in advance.
EDIT 1
It may be I can only check the identity value to a value greater than the current value ie to say 206000 ?
EDIT 2
Perhaps there is an argument that Identity value should never be reseed to less than the max PK value, even if there is 100,000 spare numbers, as one day you will get a collision.
I have a database running under Sql server 2005 with merge replication. I want to change some of the FK columns to be 'not null' as they should always have a value. SQL server won't let me do that though, this is what it says:
Unable to modify table. It is invalid to drop the default constraint
on the rowguid column that is used by
merge replication. The schema change
failed during execution of an internal
replication procedure. For corrective
action, see the other error messages
that accompany this error message. The
transaction ended in the trigger. The
batch has been aborted.
I am not trying to change the constraints on the rowguid column at all, only on another column that is acting as a FK. Other columns I want to set to be not null because the record doesn't make any sense without that information (i.e. on a customer, the customer name).
Questions:
Is there a way to update columns to be 'not null' without turning off replication then turning it back on again?
Is this even the best way to do this - should I be using a constraint instead?
Apparently SSMS makes changes to tables by dropping them and recreating them. So just needed to make the changes using T-SQL statement.
ALTER TABLE dbo.MyTable ALTER COLUMN MyColumn nvarchar(50) NOT NULL
You need to script out your change in T-SQL statements as SQL Server Management Studio will look to drop and re-create the table, as opposed to simply adding the additional column.
You will also need to add the new column to your Publications.
Please note that changing a column in this manner can be detrimental to the performance of Replication. Dependent on the size of the table you are altering, can lead to a lot of data being replicated. Consider that although your table modification can be performed in a single statement, if 1 million rows are affected then 1 million updates will be generated at the Subscriber, NOT a single update statement as is commonly thought.
The hands on, improved performance approach.......
To perform this exercise you need to:
Backup your Replication environment by scripting out your entire configuration.
Remove the table from Replication at
both Publishers/Subscribers
Add the column at each
Publisher/Subscriber.
Apply the Update locally at each
Publisher/Subscriber.
Add the table back into Replication.
Validate that transactions are being
Replicated.
To add a NOT NULL Column to a table with many records, a DEFAULT constraint needs to be applied. This constraint causes the entire ALTER TABLE command to take a long time to run if the table is very large. This is because:
Assumptions:
The DEFAULT constraint modifies existing records. This means that the db needs to increase the size of each record, which causes it to shift records on full data-pages to other data-pages and that takes time.
The DEFAULT update executes as an atomic transaction. This means that the transaction log will need to be grown so that a roll-back can be executed if necessary.
The transaction log keeps track of the entire record. Therefore, even though only a single field is modified, the space needed by the log will be based on the size of the entire record multiplied by the # of existing records. This means that adding a column to a table with small records will be faster than adding a column to a table with large records even if the total # of records are the same for both tables.
Possible solutions:
Suck it up and wait for the process to complete. Just make sure to set the timeout period to be very long. The problem with this is that it may take hours or days to do depending on the # of records.
Add the column but allow NULL. Afterward, run an UPDATE query to set the DEFAULT value for existing rows. Do not do UPDATE *. Update batches of records at a time or you'll end up with the same problem as solution #1. The problem with this approach is that you end up with a column that allows NULL when you know that this is an unnecessary option. I believe that there are some best practice documents out there that says that you should not have columns that allow NULL unless it's necessary.
Create a new table with the same schema. Add the column to that schema. Transfer the data over from the original table. Drop the original table and rename the new table. I'm not certain how this is any better than #1.
Questions:
Are my assumptions correct?
Are these my only solutions? If so, which one is the best? I f not, what else could I do?
I ran into this problem for my work also. And my solution is along #2.
Here are my steps (I am using SQL Server 2005):
1) Add the column to the table with a default value:
ALTER TABLE MyTable ADD MyColumn varchar(40) DEFAULT('')
2) Add a NOT NULL constraint with the NOCHECK option. The NOCHECK does not enforce on existing values:
ALTER TABLE MyTable WITH NOCHECK
ADD CONSTRAINT MyColumn_NOTNULL CHECK (MyColumn IS NOT NULL)
3) Update the values incrementally in table:
GO
UPDATE TOP(3000) MyTable SET MyColumn = '' WHERE MyColumn IS NULL
GO 1000
The update statement will only update maximum 3000 records. This allow to save a chunk of data at the time. I have to use "MyColumn IS NULL" because my table does not have a sequence primary key.
GO 1000 will execute the previous statement 1000 times. This will update 3 million records, if you need more just increase this number. It will continue to execute until SQL Server returns 0 records for the UPDATE statement.
Here's what I would try:
Do a full backup of the database.
Add the new column, allowing nulls - don't set a default.
Set SIMPLE recovery, which truncates the tran log as soon as each batch is committed.
The SQL is: ALTER DATABASE XXX SET RECOVERY SIMPLE
Run the update in batches as you discussed above, committing after each one.
Reset the new column to no longer allow nulls.
Go back to the normal FULL recovery.
The SQL is: ALTER DATABASE XXX SET RECOVERY FULL
Backup the database again.
The use of the SIMPLE recovery model doesn't stop logging, but it significantly reduces its impact. This is because the server discards the recovery information after every commit.
You could:
Start a transaction.
Grab a write lock on your original table so no one writes to it.
Create a shadow table with the new schema.
Transfer all the data from the original table.
execute sp_rename to rename the old table out.
execute sp_rename to rename the new table in.
Finally, you commit the transaction.
The advantage of this approach is that your readers will be able to access the table during the long process and that you can perform any kind of schema change in the background.
Just to update this with the latest information.
In SQL Server 2012 this can now be carried out as an online operation in the following circumstances
Enterprise Edition only
The default must be a runtime constant
For the second requirement examples might be a literal constant or a function such as GETDATE() that evaluates to the same value for all rows. A default of NEWID() would not qualify and would still end up updating all rows there and then.
For defaults that qualify SQL Server evaluates them and stores the result as the default value in the column metadata so this is independent of the default constraint which is created (which can even be dropped if no longer required). This is viewable in sys.system_internals_partition_columns. The value doesn't get written out to the rows until next time they happen to get updated.
More details about this here: online non-null with values column add in sql server 2012
Admitted that this is an old question. My colleague recently told me that he was able to do it in one single alter table statement on a table with 13.6M rows. It finished within a second in SQL Server 2012. I was able to confirm the same on a table with 8M rows. Something changed in later version of SQL Server?
Alter table mytable add mycolumn char(1) not null default('N');
I think this depends on the SQL flavor you are using, but what if you took option 2, but at the very end alter table table to not null with the default value?
Would it be fast, since it sees all the values are not null?
If you want the column in the same table, you'll just have to do it. Now, option 3 is potentially the best for this because you can still have the database "live" while this operation is going on. If you use option 1, the table is locked while the operation happens and then you're really stuck.
If you don't really care if the column is in the table, then I suppose a segmented approach is the next best. Though, I really try to avoid that (to the point that I don't do it) because then like Charles Bretana says, you'll have to make sure and find all the places that update/insert that table and modify those. Ugh!
I had a similar problem, and went for your option #2.
It takes 20 minutes this way, as opposed to 32 hours the other way!!! Huge difference, thanks for the tip.
I wrote a full blog entry about it, but here's the important sql:
Alter table MyTable
Add MyNewColumn char(10) null default '?';
go
update MyTable set MyNewColumn='?' where MyPrimaryKey between 0 and 1000000
go
update MyTable set MyNewColumn='?' where MyPrimaryKey between 1000000 and 2000000
go
update MyTable set MyNewColumn='?' where MyPrimaryKey between 2000000 and 3000000
go
..etc..
Alter table MyTable
Alter column MyNewColumn char(10) not null;
And the blog entry if you're interested:
http://splinter.com.au/adding-a-column-to-a-massive-sql-server-table
I had a similar problem and I went with modified #3 approach. In my case the database was in SIMPLE recovery mode and the table to which column was supposed to be added was not referenced by any FK constraints.
Instead of creating a new table with the same schema and copying contents of original table, I used SELECT…INTO syntax.
According to Microsoft (http://technet.microsoft.com/en-us/library/ms188029(v=sql.105).aspx)
The amount of logging for SELECT...INTO depends on the recovery model
in effect for the database. Under the simple recovery model or
bulk-logged recovery model, bulk operations are minimally logged. With
minimal logging, using the SELECT… INTO statement can be more
efficient than creating a table and then populating the table with an
INSERT statement. For more information, see Operations That Can Be
Minimally Logged.
The sequence of steps :
1.Move data from old table to new while adding new column with default
SELECT table.*, cast (‘default’ as nvarchar(256)) new_column
INTO table_copy
FROM table
2.Drop old table
DROP TABLE table
3.Rename newly created table
EXEC sp_rename 'table_copy', ‘table’
4.Create necessary constraints and indexes on the new table
In my case the table had more than 100 million rows and this approach completed faster than approach #2 and log space growth was minimal.
1) Add the column to the table with a default value:
ALTER TABLE MyTable ADD MyColumn int default 0
2) Update the values incrementally in the table (same effect as accepted answer). Adjust the number of records being updated to your environment, to avoid blocking other users/processes.
declare #rowcount int = 1
while (#rowcount > 0)
begin
UPDATE TOP(10000) MyTable SET MyColumn = 0 WHERE MyColumn IS NULL
set #rowcount = ##ROWCOUNT
end
3) Alter the column definition to require not null. Run the following at a moment when the table is not in use (or schedule a few minutes of downtime). I have successfully used this for tables with millions of records.
ALTER TABLE MyTable ALTER COLUMN MyColumn int NOT NULL
I would use CURSOR instead of UPDATE. Cursor will update all matching records in batch, record by record -- it takes time but not locks table.
If you want to avoid locks use WAIT.
Also I am not sure, that DEFAULT constrain changes existing rows.
Probably NOT NULL constrain use together with DEFAULT causes case described by author.
If it changes add it in the end
So pseudocode will look like:
-- without NOT NULL constrain -- we will add it in the end
ALTER TABLE table ADD new_column INT DEFAULT 0
DECLARE fillNullColumn CURSOR LOCAL FAST_FORWARD
SELECT
key
FROM
table WITH (NOLOCK)
WHERE
new_column IS NULL
OPEN fillNullColumn
DECLARE
#key INT
FETCH NEXT FROM fillNullColumn INTO #key
WHILE ##FETCH_STATUS = 0 BEGIN
UPDATE
table WITH (ROWLOCK)
SET
new_column = 0 -- default value
WHERE
key = #key
WAIT 00:00:05 --wait 5 seconds, keep in mind it causes updating only 12 rows per minute
FETCH NEXT FROM fillNullColumn INTO #key
END
CLOSE fillNullColumn
DEALLOCATE fillNullColumn
ALTER TABLE table ALTER COLUMN new_column ADD CONSTRAIN xxx
I am sure that there are some syntax errors, but I hope that this
help to solve your problem.
Good luck!
Vertically segment the table. This means you will have two tables, with the same primary key, and exactly the same number of records... One will be the one you already have, the other will have just the key, and the new Non-Null column (with default value) .
Modify all Insert, Update, and delete code so they keep the two tables in synch... If you want you can create a view that "joins" the two tables together to create a single logical combination of the two that appears like a single table for client Select statements...