并发问题，同时更新SQL Server表列

Question

I am working on accounting project and facing concurrency update issue. I have followed below scenario
1) User1 retrieves column1 data
2) User2 also retrieves column1 data
3) User1 updates the column1 data
4) while updating User2 column1 data i have to tell the user column1 data is already updated please refresh the details & update if modified from original.

and i don't want to restrict the User2 from retrieving the data which is already retrieved by User1 , how to handle this type concurrency or any builtin function available in SQL Server?

Answer 1

Reiterate your problem as I understand it:

1. User1 is retrived column1 data
2. User2 is also retrived column1 data
3. User1 is updated the column1 data
4. User2 wants to update the stale data on column1. You want to alert user 2 that the data is stale, user 2 should do a refresh (get latest value) and then can update again.

This is exactly what rowversion is for. You include this on the record as a new column. Sql server will handle assigning values and incrementing them each time data changes on the record. You should retrieve this value along with the other relevant details of that record and then include it in your update statement. If the values do not match you have a concurrency error, the record was updated in between the last time that user retrieved the data and the time they want to update the data.

Also note that in this case rowversion is altered any time any alteration is made on a record, not just for that one particular column.

Logic after implementing rowversion in the table.

1. Any user retrieves column1 data also retrieves the record's rowversion value
2. Any user updates column1 data includes the rowversion value in the WHERE clause of the UPDATE statement.
   1. If the number of records affected (updated) is 0 the update did not occur because the record was updated by another connection between the retrieve and the update. In this case execute logic to display an error message and retrieve the updated data as well as the new rowversion value. ( alternatively the record was deleted but lets assume this is not the case ).
   2. If the number of records affected (updated) was 1 then the update succeeded. The rowversion value of the record has also changed. Be sure to return the updated rowversion to the user if you want to allow additional updates without a complete data refresh.