I need to do a MERGE in Oracle, but I'm stuck.
In SQL Server, I always use the BY SOURCE and BY TARGET condition to check where record exists, and then take an action.
I'm a little confused because I don't know how to achieve the same in PL/SQL.
I need to do a MERGE on two tables (customers and customers_stage).
If the record does not exists in the customer table - then insert.
If the record exits in both - then update.
If the record does not exists in customers_stage - then delete.
In SQL Server, it would look like this:
MERGE INTO dbo.Customers AS target
USING dbo.Customers_stage AS source ON target.ID = source.ExternalID
WHEN NOT MATCHED BY TARGET
THEN
INSERT
WHEN MATCHED
THEN
UPDATE
WHEN NOT MATCHED BY SOURCE
THEN
DELETE
How to achieve the same functionality in Oracle? I use SQL Developer.
Thank you very much.
Related
I am looking for a reject link type of solution in a dedup scenario. For example in the following code:
MERGE
temp.many_random t
USING
( SELECT DISTINCT * FROM temp.many_random WHERE d=CURRENT_DATE() )
ON FALSE
WHEN NOT MATCHED
BY SOURCE AND d=CURRENT_DATE() THEN DELETE
WHEN NOT MATCHED BY TARGET THEN INSERT ROW
Can I replace THEN DELETE with something like INSERT INTO TABLE (different than the compare tables) so that we can capture these rejects and troubleshoot for pipeline analysis?
If I understand the problem, you want the result of a MERGE query to write to 2 different tables.
Since MERGE can't do that, I'll suggest to write 2 queries:
One that does whatever the primary query is doing.
A second almost identical one, but that writes the wrong records to a different table.
So there's this table of just about 40,000 rows I am looking to update. Colleague said it's best to incrementally update the table instead of complete delete and load.
So I've tried hashing out the design and logic of a script to do this, but my inexperience is getting to me. I just don't know what's efficient and unneeded to incrementally update a table.
Currently, the warehouse looks like this: data comes from source into a table (let's call this T1) in Teradata. Then it's sent into another table (let's call this T2) in Teradata with some added fields such as timestamp. Lastly, a view is built on that last table for security reasons.
So with that laid out, I was thinking of creating a temp/volatile table with data from T1. This would have all the data up to the time the script is run with new records. Then, go through the entire table seeing if the ID (primary index) already exists in T2, and if not, add it to another temp table. Then somehow combine the second temp table with T2 and override T2 and build a view on top of that.
Does this make any sense?
There's also the possibility of records being updated. So they would already exist in T2, but have updated data in a new version of T1. I think comparing the values of all the columns from T1 to T2 would be highly inefficient, but can't think of another way to do this
A 40,000 row delete and insert should be pretty painless for any modern database. Ditto for updates.
The real reason for doing and incremental delete/update/insert is so you can log the changes and timestamp rows in the permanent table with the date/time of nsertion and/or last update. The usual technique goes something like this:
remove rows from the permanent table that don't exist in the temp table
update rows that exist in both tables
insert rows that exist in the temp table, but don't exist in the permanent table.
Looking at the Teradata docs, that would be something like this (no warranties about this being syntactically correct, since I don't have a Teradata instance to play with):
delete permanent p
where not exists ( select *
from temp t
where t.id = p.id
)
update p
from permanent p ,
temp t
set ...
where t.id = p.id
insert permanent
select ...
from temp t
where not exists ( select *
from permanent p
where p.id = t.id
)
One might note that the deletes might get a little hairy if there are dependent foreign key constraints involved.
One might also note that on the update, the where clause might get a tad...complicated if you want to check for actual changes to column values: not much point in updating a row if nothing has changed.
There's a Teradata MERGE command that you might find useful, check this post:
https://forums.teradata.com/forum/database/merge-syntax-simple-version
merge into merge_tmp as t using (select 1 as a,'stf' as b,'uuj' as c) as s
on t.a = s.a
when matched then update set c = s.c
when not matched then insert values (s.a,s.b,s.c);
If you need to match on more columns simple put an and in the on statement.
Edit: If you want to use MERGE you might also need to use a delete statement like the one in nicholas' post.
I am stuck with a problem with different views.
Present Scenario:
I am using SSIS packages to get data from Server A to Server B every 15 minutes.Created 10 packages for 10 different tables and also created 10 staging table for the same. In the DataFlow Task it is selecting data from server A with ID greater last imported ID and dumping them onto a Staging table.(Each table has its own stagin table).After the DataFlow task I am using a MERGE statement to merge records from Staging table to Destination table where ID is NO Matched.
Problem:
This will take care all new records inserted but if once a record is picked by SSIS job and is update at the source I am not able to pick it up again and not able to grab the updated data.
Questions:
How will I be able to achieve the Update with impacting the source database server too much.
Do I use MERGE statement and select 10,000 records every single run?(every 15 minutes)
Do I use LookUp transformation to do the updates
Some tables have more than 2 million records and growing, so what is the best approach for them.
NOTE:
I can truncate tables in destination and reinsert complete data for the first run.
Edit:
The Source has a column 'LAST_UPDATE_DATE' which I can Use in my query.
If I'm understanding your statements correctly it sounds like you're pretty close to your solution. If you currently have a merge statement that includes the insert (where source does not match destination) you should be able to easily include the update statement for the (where source matches destination).
example:
MERGE target_table as destination_table_alias
USING (
SELECT <column_name(s)>
FROM source_table
) AS source_alias
ON
[source_table].[table_identifier] = [destination_table_alias].[table_identifier]
WHEN MATCHED THEN UPDATE
SET [destination_table_alias.column_name1] = mySource.column_name1,
[destination_table_alias.column_name2] = mySource.column_name2
WHEN NOT MATCHED THEN
INSERT
([column_name1],[column_name2])
VALUES([source_alias].[column_name1],mySource.[column_name2])
So, to your points:
Update can be achieved via the 'WHEN MATCHED' logic within the merge statement
If you have the last ID of the table that you're loading, you can include this as a filter on your select statement so that the dataset is incremental.
No lookup is needed with the 'WHEN MATCHED' is utilized.
utilizing a select filter in the select portion of the merge statement.
Hope this helps
I'm using Sql server 2012
Just curious if there is a way to do such a thing...
My update query looks like
UPDATE a
SET a.TowerNumber=b.SiteNumber
FROM tower a
INNER JOIN sites b
ON a.sitenumber = b.sitenumber
what i would like to do after the ON line is something like
EDIT **select records that did not match the ON statement**
thanks in advance
This query returns all rows that wouldn't be touched by the update because the ON (join) criteria wasn't met.
SELECT *
FROM tower
WHERE sitenumber NOT IN
(SELECT sitenumber
FROM sites)
I think you can try to use an INSTEAD OF trigger and then make use of the DELETED table. It should contain the rows that were updated during the update operation so what you are looking after are the rest of the rows in the initial table (select rows from your table where not in DELETED table)
Can the UPDATE query be used without a WHERE clause? And if so in what conditions?
if you don't use the WHERE clause all the records on the table will be affected
So, I think when you want to update the whole field for some kind of reasons like updating the status of users enrollment to free for all users.
UPDATE users SET status = "free";
The UPDATE statement in SQL is used to update records in the table. We can modify one or multiple records (rows) in a table using UPDATE statement. If you do not use WHERE clause in UPDATE statement, all the records in the table will be updated.