Sql updating multiple tables simultaneously
In general, the vast majority of queries only use inner joins and left joins, but it’s crucial to understand their relationship with cross joins as well to understand how you should ensure that the join produces at most one output row for each row to be modified.In other words, a target row shouldn’t join to more than one row from the other table(s).While this is certainly something to watch out for, more commonly we might just want to join in a table to decide which rows we want to update.Suppose we only want to update rows in queries involving multiple tables can be quite difficult to write correctly.In this example I will take a Products table as the target table and Updated Products as the source table containing an updated list of products. I will then use the MERGE command to synchronize the target table with the source table. In this tip we will walk through how to use the MERGE statement and do this in one pass.Beginning with SQL Server 2008, you can use MERGE command to perform these operations in a single statement.
Though it seems to be straight forward at first glance, it becomes cumbersome when you have do it very often or on multiple tables, even the performance degrades significantly with this approach.A recent product update required a data migration that left us scratching our heads trying to figure out why our queries weren’t working.We’ll provide some context about the schema of the table we were modifying, explain the changes we needed to make, then explain how we used boolean algebra to help debug the issue.You then specify the type of data modification that is to occur when the records between the two data are matched or are not matched. MERGE is very useful, especially when it comes to loading data warehouse tables, which can be very large and require specific actions to be taken when rows are or are not present.