Archive for Query

ORACLE SQL for EPM tips and tricks S01EP03!

Posted in Query, SQL, Tips and Tricks with tags , , on March 26, 2019 by radk00

Hi all! Continuing the Oracle SQL for EPM series, today’s post is quite simple, but it may consume an extreme amount of time when we are requested to troubleshoot “why these numbers does not match” type of scenarios. Its related to UNION and UNION ALL operations. Let me describe what happened to me in one of those situations.

The client had a table with several columns that would calculate some metrics related to their

business. It was a “cumulative” type of table, where metrics were being aggregated by each previous period’s numbers. In a very resumed way, lets use the following example:

1

So, for Feb-19, the SUM would be 150 for Account 1 and 60 for Account 2. Next month, he would get the following:

2

His logic was summing the March period in Account 1 correctly (30) and summing it to previous 150. However, since Account 2 was not coming in March, his SQL was not reporting Account 2 in March. To make the calculations easier, he decided to add a “dummy” metric for all existing Accounts as 0, so his logic would calculate it correctly even it the record did not exist for that period. Something like that:

3

The process would still give his correct value of 30 in Account 1 for March and 0 for Account 2, which would then sum against the previous periods. It all worked fine, until someday someone complained that the numbers could not be right and some numbers were missing. When I checked the code, I quickly realized his mistake: he created his “dummy” metrics using a UNION in Oracle against his periodic metric and his “dummy” metric. But why it was giving the wrong numbers? Oracle explains:

  • UNION combines the results of two queries, which eliminates duplicate selected rows. The UNION operator returns only distinct rows that appear in either result.

Let’s picture the problem. His logic worked fine for Feb and Mar, but in Apr, something like this happened:

4

If you sum Apr period for Account 1, the number should 80, but he was getting only 60 as below:

5

This is due to UNION’s behavior: It will run an implicit distinct in the combined dataset, which in this case is eliminating good data. I went ahead and changed the UNION to UNION ALL, which Oracle states:

  • The UNION operator returns only distinct rows that appear in either result, while the UNION ALL operator returns all rows. The UNION ALL operator does not eliminate duplicate selected rows.

The result is the following:

6

Now it looks correct: 80 for Account 1 and 0 for Account 2.

That’s it folks! Simple things that may give us enormous headaches and wrong numbers, so please always check out when you see an UNION in the queries! It may be implicitly omitting some good data there.

See ya!

ORACLE SQL for EPM tips and tricks S01EP02!

Posted in ACE, Connect By, EPM, Oracle Database, Performance, Query, SQL, Tips and Tricks, WITH Clause with tags , , , , , , , on March 21, 2019 by RZGiampaoli

hey guys how are you? Let’s continue the SQL for EPM series. Today I’ll continue to talk about With with a small bonus of Connect by :). let’s start.

A lot of people uses Connect By in a daily bases but as far I having seeing, most of then don’t know how to use it properly. I already lost count with the amount of people complaining about performance issue with Connect By.

The thing is, Connect By works a little different than everything else in Oracle. We can say that Connect By has 2 stages and we’ll see why I’m saying that with this example. Let’s get back to our metadata table and let’s do a Connect By to extract the Balance Sheet Hierarchy from the Juno application:

As we can see, inside this table we have more than one application and more than one hierarchies for each application. That’s ok, we just need to filter it in our SQL right?

If we filter the APP_NAME and the HIER_NAME we’ll get all accounts for that Application and this will generate 12,622 rows. By the way, this table has all metadata from all our applications and we always filter by APP_NAME and HIER_NAME to select what we want (the table is also partitioned and sub-partitioned by these 2 columns). It’s important to know that without filtering anything this table has:

Ok, now, if we want to get just the BS hierarchy we just need to do the Connect By right?

That works… perfect… or not? Well in fact, this the wrong way to use Connect by because what I said before, the 2 stages.

As you can see, this query took 25 sec just to return the first 50 rows. In a integration this will take way more time, in fact, if you join this table to a data table to do a SUM in the BS level, this will take ages to return.

The reason is that for the Connect by, first Oracle does everything that is after the word Connect by and after the word Start with and then, and only then, it does what is in the where condition. That means, first he did the connect by in those 2.260.372 rows (and they are all repeated) and then after all the processing, it filtered what we wanted, that is the APP_NAME and the HIER_NAME. Then the right way to use it is:

Now it looks way better. 0.375 seconds to do exactly the same thing as before, and the only thing I did was to move our filters to the right place. Now Oracle is filtering and doing the Connect by at same time.

Now, if you do a SYS_CONNECT_BY_PATH and want to get just the leaf (to have the complete path that the hierarchy does, you can filter the leafs in the where clause (and need to be there otherwise it’ll not have the entire hierarchy during the connect by). This is how:

Now you see that the connect by filtered what needs to be filter during the Connect by execution and afterwards, it filtered just the leafs (using the CONNECT_BY_ISLEAF that returns if a member is a leaf or not).

Also, i used the CONNECT_BY_ROOT to generate the Root member used in this query (BS) and the SYS_CONNECT_BY_PATH to generate the entire path of the metadata (Very useful to transform parent/child tables in generation tables using this Technic and a regexp [we’ll see this in another post]).

Ok, now that the “Bonus” is written, let’s talk about the WITH that was the main subject here. Even with this Connect by write in the right way with the filters in the right place, we can still improve the performance using WITH.

That’s right, the idea is to prepare our subset of data using WITH before we ask Oracle to do the Connect by and leave it as simple as possible. Let’s take a look:

This is by far the best way to use a Connect by clause. You can, instead of using WITH use a sub-query but I think this way is easier and more organised as well. Also, I know the time difference doesn’t look to big between the previous example and this one but when you join this with data and start to SUM everything, you’ll see a huge difference between this method and the previous one.

Also, some times Oracle get lost with the previous method making everything slower but with the WITH method, it never happens then I advise you start to use this.

I hope you guys enjoy this little tip and see you next time.

ORACLE SQL for EPM tips and tricks S01EP01!

Posted in DEVEPM, ETL, Oracle, Oracle Database, Performance, SQL, Tips and Tricks, Uncategorized, WITH Clause with tags , , , , , , on January 21, 2019 by RZGiampaoli

Hey guys how are you? I decide to start a new series called ORACLE SQL for EPM tips and tricks. The idea here is to show the most useful SQL commands for EPM, how to improve performance, tips, tricks and everything that can be useful from a SQL point of view!

And to start well, I’ll show something very old but very useful that I don’t see too many people using these days. “WITH” clause.

I love to use “WITH” in my code. It helps organize the code, helps to optimize it and more important, to make it more efficient.

When you use “WITH” Oracle treats your query inside it as an inline view or resolved as a temporary table, making it easier and faster for Oracle to access that data if you need it again.

Simply putting, every time you needs to right a query that uses the same table over and over, it’ll probably be way more efficient if you use “WITH”.

The “WITH”clause works a little bit different from a regular SQL. We can say that we split the query in 2, one is the “WITH” declaration (That will behave like a table) and the other is the SQL that will Query the “WITH”.

WITH name_of_temp_table_here AS
(
    YOUR QUERY HERE
),
   name_of_temp_table_here2 AS
(
   SELECT *
   FROM name_of_temp_table_here, another_table...
)
SELECT *
FROM name_of_temp_table_here, name_of_temp_table_here2 

In the “WITH” you can have any kind of query you want. You can do joins, group by, you can also have more than one “WITH”, you can use the result of one “WITH” in the next “WITH”, you can do a lot of things.

But for now, lets take a look in a more real example. Let’s say that you have a table like I do, that contains all metadata from all yours applications:

Let’s say you want to get the Parent of a attribute that is associated with your Entity dimension. You probably will be doing something like this:

In the “FROM” we call the table 2 times and we join and filter everything we need. Since we don’t have attribute association in all levels we do a “Left Join” to make sure all Entities comes in the query. If we run a Explain Plan now we’ll get something like this:

As you can see, Oracle is querying the METADATA_EXTRACT table twice and each time it’s doing a FULL in one Partition (‘ENTITY’ and ‘PHYSICAL_GEOGRAPHY’ partitions).

Now, if we change the query (and we can do it in different ways, this is just one of them) to a “WITH” clause we ‘ll have something like this:

As you can see, we achieved the same results with the code a little bit different. Now I have all my filters in the “WITH” query and in the bottom I just call the “WITH” query 2 times and do what needs to be done.

If we run a Explain Plain now we will have:

As you can see, Oracle now is querying the METADATA_EXTRACT table just once and then his queries the SYS.SYS TEMP table twice. The only problem with this query and the way I did is that since we are creating a temporary table filtering 2 partitions and then later I’m filtering again, it’s basically doing 2 FULL scan in the same TEMP table, and even so, it’s a few seconds faster then the original query.

But this is just an example on how we can reduce the amount of times that Oracle needs to query a table. WITH is not a miracle clause or anything like that, is just another tool that we can use to optimize our code, and its performance needs to be evaluated in a case-by-case basis.

And even if the performance doesn’t change, I believe using “WITH” clause makes any query easier to ready, to test, to update and to right since you can divide your huge query in small bits and then join
everything in the bottom query.

“WITH” is a huge subject and we’ll be talking more about it in the next post, and this time we’ll be improving performance as well using “WITH” with “CONNECT BY”.