Particularly, if we are working on the performance of the update query, we should take into account of this probability. The following execution plan illustrates an execution plan of the previous query. The only difference is that this query updated the 3. This query was completed within 68 seconds.
We added a non-clustered index on Persons table before to update and the added index involves the PersonCityName and PersonPostCode columns as the index key.
The following execution plan is demonstrating an execution plan of the same query, but this query was completed within seconds because of the added index, unlike the first one. We have seen this obvious performance difference between the same query because of index usage on the updated columns. As a result, if the updated columns are being used by the indexes, like this, for example, the query performance might be affected negatively.
In particular, we should consider this problem if we will update a large number of rows. To overcome this issue, we can disable or remove the index before executing the update query.
On the other hand, a warning sign is seen on the Sort operator, and it indicates something does not go well for this operator. When we hover the mouse over this operator, we can see the warning details. During the execution of the query, the query optimizer calculates a required memory consumption for the query based on the estimated row numbers and row size. However, this consumption estimation can be wrong for a variety of reasons, and if the query requires more memory than the estimation, it uses the tempdb data.
This mechanism is called a tempdb spill and causes performance loss. The reason for this: the memory always faster than the tempdb database because the tempdb database uses the disk resources. Now, if we go back to our position, the MERGE statement can be used as an alternative method for updating data in a table with those in another table. In this method, the reference table can be thought of as a source table and the target table will be the table to be updated.
The following query can be an example of this usage method. We have typed the Persons table after the MERGE statement because it is our target table, which we want to update, and we gave Per alias to it in order to use the rest of the query.
With the help of this syntax, the join condition is defined between the target and source table. In this last line of the query, we chose the manipulation method for the matched rows. Finally, we added the semicolon ; sign because the MERGE statements must end with the semicolon signs.
With the above understanding, you can modify the set fields and "on" criteria to do your work. You can also perform the checks, then pull the data into the temp table s and then run the update using the above syntax replacing your table and column names.
I found this question in looking for my own solution to a very complex join. This is an alternative solution, to a more complex version of the problem, which I thought might be useful.
Those SKUs are then stored in a different table. I found that that was too complex to incorporate into a SELECT within mysql, so I created a temporary table, and joined that with the update statement I had an issue with duplicate entries in one table itself. Below is the approaches were working for me. It has also been advocated by sibaz.
The best thing is create temporary table from the query, then use the temporary table to update as one query. Stack Overflow for Teams — Collaborate and share knowledge with a private group.
Create a free Team What is Teams? Collectives on Stack Overflow. Learn more. Asked 12 years, 5 months ago. Active 2 months ago. Viewed 1. If the first event completes before the second event then I would like to link them up.
John M John M I am not sure what you are asking? Are you trying to figure out how to do an update with a SQL Select? Add a comment. Active Oldest Votes. Valerian Pereira 1 1 gold badge 6 6 silver badges 16 16 bronze badges. Eric Eric The first form update with join is going to be a lot more efficient than the second.
The first would do a single join, whereas the second would execute the select query for every row of tableA. For the first example, shouldn't you use an inner join? Cerin yea that happened to me.
Thilo Thilo k 94 94 gold badges silver badges bronze badges. There is an exemple an update of a join in another SO : stackoverflow. It's generally called view updating. Add a comment. Active Oldest Votes. DNAME appears in the subquery. Tony Andrews Tony Andrews k 20 20 gold badges silver badges bronze badges. Just updating the result of a select statement. There is also a from which also returning of values called Update with returning clause And some specifics for updates with nested tables.
Thilo k 94 94 gold badges silver badges bronze badges. Thanks for comments, I thought this was standard Sql ID SET t1. Andomar Andomar k 44 44 gold badges silver badges bronze badges. Are you sure that works? Using dpriver. I'm not sure it is standard SQL either.
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