I've an UPDATE
statement which can update more than million records. I want to update them in batches of 1000 or 10000. I tried with @@ROWCOUNT
but I am unable to get desired result.
Just for testing purpose what I did is, I selected table with 14 records and set a row count of 5. This query is supposed to update records in 5, 5 and 4 but it just updates first 5 records.
Query - 1:
SET ROWCOUNT 5
UPDATE TableName
SET Value = 'abc1'
WHERE Parameter1 = 'abc' AND Parameter2 = 123
WHILE @@ROWCOUNT > 0
BEGIN
SET rowcount 5
UPDATE TableName
SET Value = 'abc1'
WHERE Parameter1 = 'abc' AND Parameter2 = 123
PRINT (@@ROWCOUNT)
END
SET rowcount 0
Query - 2:
SET ROWCOUNT 5
WHILE (@@ROWCOUNT > 0)
BEGIN
BEGIN TRANSACTION
UPDATE TableName
SET Value = 'abc1'
WHERE Parameter1 = 'abc' AND Parameter2 = 123
PRINT (@@ROWCOUNT)
IF @@ROWCOUNT = 0
BEGIN
COMMIT TRANSACTION
BREAK
END
COMMIT TRANSACTION
END
SET ROWCOUNT 0
What am I missing here?
This question is related to
sql-server
First of all, thank you all for your inputs. I tweak my Query - 1
and got my desired result. Gordon Linoff is right, PRINT
was messing up my query so I modified it as following:
Modified Query - 1:
SET ROWCOUNT 5
WHILE (1 = 1)
BEGIN
BEGIN TRANSACTION
UPDATE TableName
SET Value = 'abc1'
WHERE Parameter1 = 'abc' AND Parameter2 = 123
IF @@ROWCOUNT = 0
BEGIN
COMMIT TRANSACTION
BREAK
END
COMMIT TRANSACTION
END
SET ROWCOUNT 0
Output:
(5 row(s) affected)
(5 row(s) affected)
(4 row(s) affected)
(0 row(s) affected)
WHILE EXISTS (SELECT * FROM TableName WHERE Value <> 'abc1' AND Parameter1 = 'abc' AND Parameter2 = 123)
BEGIN
UPDATE TOP (1000) TableName
SET Value = 'abc1'
WHERE Parameter1 = 'abc' AND Parameter2 = 123 AND Value <> 'abc1'
END
This is a more efficient version of the solution from @Kramb. The existence check is redundant as the update where clause already handles this. Instead you just grab the rowcount and compare to batchsize.
Also note @Kramb solution didn't filter out already updated rows from the next iteration hence it would be an infinite loop.
Also uses the modern batch size syntax instead of using rowcount.
DECLARE @batchSize INT, @rowsUpdated INT
SET @batchSize = 1000;
SET @rowsUpdated = @batchSize; -- Initialise for the while loop entry
WHILE (@batchSize = @rowsUpdated)
BEGIN
UPDATE TOP (@batchSize) TableName
SET Value = 'abc1'
WHERE Parameter1 = 'abc' AND Parameter2 = 123 and Value <> 'abc1';
SET @rowsUpdated = @@ROWCOUNT;
END
I want share my experience. A few days ago I have to update 21 million records in table with 76 million records. My colleague suggested the next variant. For example, we have the next table 'Persons':
Id | FirstName | LastName | Email | JobTitle
1 | John | Doe | [email protected] | Software Developer
2 | John1 | Doe1 | [email protected] | Software Developer
3 | John2 | Doe2 | [email protected] | Web Designer
Task: Update persons to the new Job Title: 'Software Developer' -> 'Web Developer'.
1. Create Temporary Table 'Persons_SoftwareDeveloper_To_WebDeveloper (Id INT Primary Key)'
2. Select into temporary table persons which you want to update with the new Job Title:
INSERT INTO Persons_SoftwareDeveloper_To_WebDeveloper SELECT Id FROM
Persons WITH(NOLOCK) --avoid lock
WHERE JobTitle = 'Software Developer'
OPTION(MAXDOP 1) -- use only one core
Depends on rows count, this statement will take some time to fill your temporary table, but it would avoid locks. In my situation it took about 5 minutes (21 million rows).
3. The main idea is to generate micro sql statements to update database. So, let's print them:
DECLARE @i INT, @pagesize INT, @totalPersons INT
SET @i=0
SET @pagesize=2000
SELECT @totalPersons = MAX(Id) FROM Persons
while @i<= @totalPersons
begin
Print '
UPDATE persons
SET persons.JobTitle = ''ASP.NET Developer''
FROM Persons_SoftwareDeveloper_To_WebDeveloper tmp
JOIN Persons persons ON tmp.Id = persons.Id
where persons.Id between '+cast(@i as varchar(20)) +' and '+cast(@i+@pagesize as varchar(20)) +'
PRINT ''Page ' + cast((@i / @pageSize) as varchar(20)) + ' of ' + cast(@totalPersons/@pageSize as varchar(20))+'
GO
'
set @i=@i+@pagesize
end
After executing this script you will receive hundreds of batches which you can execute in one tab of MS SQL Management Studio.
4. Run printed sql statements and check for locks on table. You always can stop process and play with @pageSize to speed up or speed down updating(don't forget to change @i after you pause script).
5. Drop Persons_SoftwareDeveloper_To_AspNetDeveloper. Remove temporary table.
Minor Note: This migration could take a time and new rows with invalid data could be inserted during migration. So, firstly fix places where your rows adds. In my situation I fixed UI, 'Software Developer' -> 'Web Developer'.
Your print
is messing things up, because it resets @@ROWCOUNT
. Whenever you use @@ROWCOUNT
, my advice is to always set it immediately to a variable. So:
DECLARE @RC int;
WHILE @RC > 0 or @RC IS NULL
BEGIN
SET rowcount 5;
UPDATE TableName
SET Value = 'abc1'
WHERE Parameter1 = 'abc' AND Parameter2 = 123 AND Value <> 'abc1';
SET @RC = @@ROWCOUNT;
PRINT(@@ROWCOUNT)
END;
SET rowcount = 0;
And, another nice feature is that you don't need to repeat the update
code.
Source: Stackoverflow.com