ID — Ali NajafZadeh. Add a comment. Active Oldest Votes. Dai k 24 24 gold badges silver badges bronze badges. Robin Day Robin Day If you are editing the the link between tables SET Table. CharlesWood yeah. I have the same question in MySQL. It would be great if someone knows how to implement it to MySQL and share with everyone. How do I use an alias in set? Sebastian covers a technique for this in a recent blog post: sqlity. Show 3 more comments. This was around 10x quicker than the equivalent update Merge bugs: mssqltips.
Your point? Show 5 more comments. DDiamond 1, 2 2 gold badges 6 6 silver badges 17 17 bronze badges. Jamal Jamal 7, 1 1 gold badge 11 11 silver badges 2 2 bronze badges. By far the simplest! This will tend to work across almost all DBMS which means learn once, execute everywhere. If that is more important to you than performance you might prefer this answer, especially if your update is a one off to correct some data.
So better than Robin Day's answer for this purpose. Thanks for sharing! Peter Mortensen This assumes none of the columns are nullable though. You're right, I was typing the example by hand. I've added a third and fourth clause to the where statement to deal with that.
Col1, T1. Please visit our Privacy Statement for additional information. Tweet Share Share. City, e. Replace the select keyword with update. Specify the table name or alias name that needs to be updated. PostCode , e. If the subquery finds a matching row, the update query updates the records for the specific employee.
Therefore, if we require updating multiple columns of data, we need separate SQL statements. You cannot use ntext , text , and image data types in the subquery.
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. There are many database diagramming tools that are not only incredibly useful but also free.
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