Sql updating multiple tables simultaneously curiousdating com
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 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.
The filtering pass for condition occurs at a different time in each query, and operates over different intermediate results, so it’s easy to see how the two queries are not equivalent.
In a typical data warehousing application, quite often during the ETL cycle you need to perform INSERT, UPDATE and DELETE operations on a target table by matching the records from the source table.
For example, a products dimension table has information about the products and you need to sync-up this table with the latest information about the products from the source table.
Tr_Num SET = 1 where case when rest.class ='AC I' then res.book=1 when rest.class ='AC II' then res.book=1 when rest.class ='AC III' then res.book=1 end UPDATE res INNER JOIN rest ON = rest. PNR = 5; However, and maybe I misunderstand, but I suspect what you really want to do is actually an INSERT an UPDATE in a single transaction. Other DB sessions looking at the tables will always see the results of either none or all of the updates in the transaction (assuming you're not using the non-default transaction isolation level).
Tr_Num SET = 1, = 21 WHERE (rest.class ='AC I' OR rest.class ='AC II' OR rest.class ='AC III') AND rest.
In this tip we will walk through how to use the MERGE statement and do this in one pass.