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Will SQL update a record if there is no change to the record?
For examople, is it more efficient to replace
UPDATE TABLE myTable
Set Col1 = ISNULL(Col1,'')
...
Set Col100 = ISNULL(Col30,'')
with
UPDATE TABLE myTable
Set Col1 = ISNULL(Col1,'')
...
Set Col100 = ISNULL(Col30,'')
WHERE
Col1 IS NULL OR
...
Col30 IS NULL
214
there will be occasions where two users will both read the same data into memory. User 1 will update the data and write those changes back to the database before user 2 does the same thing. Now you have a concurrency control conflict because user 1 read the data before user 2 wrote it back to the database.
If you tell SQL Server to UPDATE some rows - it will update those rows. SQL Server doesn't do any "matching" of its own. That's up to you - you control the WHERE clause for the UPDATE . If you want to avoid updating some rows - make sure the WHERE clause excludes them.
The UPDATE statement in SQL is used to update the data of an existing table in database. We can update single columns as well as multiple columns using UPDATE statement as per our requirement.
To get the last updated record in SQL Server: We can write trigger (which automatically fires) i.e. whenever there is a change (update) that occurs on a row, the “lastupdatedby” column value should get updated by the current timestamp.
Yes, it will attempt overwrite.
117
You have to control it manually, in the where clause you can put all the fields if they are differ the new values, and where the id of your table is equals to your parameter, you will ensure that only modified records will be updated.
UPDATE table
SET field1 = @field1,
field2 = @field2
WHERE field1 != @field1 AND
field2 != @field2 AND
id = @id
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