When we fire a SQL query like
SELECT * FROM SOME_TABLE_NAME under ORACLE
What exactly happens internally? Is there any parser at work? Is it in C/C++ ?
Can any body please explain ?
Thanks in advance to all.
Short answer is yes, of course there is a parser module inside Oracle that interprets the statement text. My understanding is that the bulk of Oracle's source code is in C.
For general reference:
Any SQL statement potentially goes through three steps when Oracle is asked to execute it. Often, control is returned to the client between each of these steps, although the details can depend on the specific client being used and the manner in which calls are made.
(1) Parse -- I believe the first action is actually to check whether Oracle has a cached copy of the exact statement text. If so, it can save the work of parsing your statement again. If not, it must of course parse the text, then determine an execution plan that Oracle thinks is optimal for the statement. So conceptually at least there are two entities at work in this phase -- the parser and the optimizer.
(2) Execute -- For a SELECT statement this step would generally run just enough of the execution plan to be ready to return some rows to the client. Depending on the details of the plan, that might mean running the whole thing, or might mean doing just a very small fraction of the work. For any other kind of statement, the execute phase is when all of the work is actually done.
(3) Fetch -- This is when rows are actually returned to the client. Generally the client has a predetermined fetch array size which sets the maximum number of rows that will be returned by a single fetch call. So there may be many fetches made for a single statement. Of course if the statement is one that cannot return rows, then there is no fetch step necessary.
Manasi,
I think internally Oracle would have its own parser, which does parsing and tries compiling the query. Think its not related to C or C++.
But need to confirm.
-Justin Samuel.
Related
I have a port 'Number_1' in expression transformation in Informatica. I connected the Number_1 port to a target sql table. I need to generate number for this port 'Number_1' every time i run the mapping starting from 1 till 999. once it reaches 999 then again the value of the Number_1 should reset to 1. I'm aware there is sequence generator trans. but i need to call Sequence function from SQL server. how to achieve above?
Create a stored procedure in sql server then use stored procedure tranformation to call this from Informatica
You may call it using Stored Procedure transfomation. You may also use a stored procedure as SQL Override on Source Qualifier, however...
I hope you know what you're doing, as this is in general a very bad idea. Each call requires communication between Intergration Service and database - this will cause huge delays. Therefore it's much better to use Informatica's Sequence Generator or - even better perhaps, if all you need is an integer port with round robin - a simple expression variable.
While maciejg says makes a lot of sense performance wise - however I've known a fair few people who were more comfortable using the native database sequencer than the inbuilt one ( even some Informatica specialists ).
The thing with Informatica sequencer is how much flexibility they give and when they get set wrong it can lead to unexpected numbers being picked.
One example I have is for a sequencer being used to create unique keys in a table - if you persist the value between sessions then it works fine until you select the incorrect option while reimporting the mapping.
If you choose to lookup your previous ending value from a config file / table and add the value produced by the sequencer to this then one day when someone by mistake sets the sequencer to persist values between runs you'll all of a sudden skip that many numbers in the sequence each time the session is restarted. Native db sequencers are very basic making them very predictable and fool proof
After going through the documentations of Utplsql 3.0.2 , I couldn't find any references the assertion api as available in the older versions. Please let me know whether is there a equivalent assertion like utassert.eqtable available in newer versions.
I have just recently gone through the same pain. Most utPLSQL examples out there are for utPLSQL v2. It transpires appears that the assertions have been deprecated, and have been replaced by "Expects". I found a great blog post by Jacek Gebal that describes this. I've tried to put this and other useful links a page about how unit testing fits into Redgate's Oracle DevOps pipeline (I work for Redgate and we often get asked how to best implement automated unit testing for Oracle).
I don't think you can compare tables straight away, but you can compare cursors, which is quite flexible, because you can, for instance, set-up a cursor with test data based on a dual query, and then check that against the actual data in the table, something like this:
procedure TestCursorExample is
v_Expected sys_refcursor;
v_Actual sys_refcursor;
begin
-- Arrange (Nothing really to arrange, except setting the expectation).
open v_Expected for
select 'me#example.com' as Email
from dual;
-- Act
SomeUpsertProc('me', 'me#example.com');
-- Assert
open v_Actual for
select Email
from Tbl_User
where UserName = 'me';
ut.expect(v_Actual).to_equal(v_Expected);
end;
Also, the example above works in Oracle 11, but if you're in 12c, apparently things got even easier, because you can use the table operator with locally defined types.
I've used a similar solution to verify that certain columns of a row were updated, while others were not. You can easily open a cursor for the original data, with some columns replaces by the new fixed values. Then do the update. Then open a cursor with the new actual data of all columns. You still have to write the queries, but it's way more compact than querying everything into variables and comparing those individually.
And, because you can open the 'expected' cursor before doing the actual 'act' step of the test, you can be sure that the query with 'expected' data is not affected by the test itself, and can even base that cursor on the data you are going to modify.
For comparing the data, the cursors are serialized to XML. This may have some side effects. In the test example above, my act step didn't actually do anything, so I got this difference, showing the count as well as showing the missing data.
If your cursors have more columns, and multiple difference, it can sometimes take a seconds to spot the differences between the XML tags. Also, there are currently some edge-case issues with this, I think because of how trimming works in XML.
1) testcursorexample
Actual: refcursor [ count = 0 ] was expected to equal: refcursor [ count = 1 ]
Diff:
Rows: [ 1 differences ]
Row No. 1 - Missing: <EMAIL>me#example.com</EMAIL>
at "MySchema.MyTestPackage", line 410 ut.expect(v_Actual).to_equal(v_Expected);
See also: 'comparing cursors' from utPLSQL 3 concepts
I use Stata since several years now, along with other languages like R.
Stata is great, but there is one thing that annoys me : the generate/replace behaviour, and especially the "... already defined" error.
It means that if we want to run a piece of code twice, if this piece of code contains the definition of a variable, this definition needs 2 lines :
capture drop foo
generate foo = ...
While it takes just one line in other languages such as R.
So is there another way to define variables that combines "generate" and "replace" in one command ?
I am unaware of any way to do this directly. Further, as #Roberto's comment implies, there are reasons simply issuing a generate command will not overwrite (see: replace) the contents of a variable.
To be able to do this while maintaining data integrity, you would need to issue two separate commands as your question points out (explicitly dropping the existing variable before generating the new one) - I see this as method in which Stata forces the user to be clear about his/her intentions.
It might be noted that Stata is not alone in this regard. SQL Server, for example, requires the user drop an existing table before creating a table with the same name (in the same database), does not allow multiple columns with the same name in a table, etc. and all for good reason.
However, if you are really set on being able to issue a one-liner in Stata to do what you desire, you could write a very simple program. The following should get you started:
program mkvar
version 13
syntax anything=exp [if] [in]
capture confirm variable `anything'
if !_rc {
drop `anything'
}
generate `anything' `exp' `if' `in'
end
You then would naturally save the program to mkvar.ado in a directory that Stata would find (i.e., C:\ado\personal\ on Windows. If you are unsure, type sysdir), and call it using:
mkvar newvar=expression [if] [in]
Now, I haven't tested the above code much so you may have to do a bit of de-bugging, but it has worked fine in the examples I've tried.
On a closing note, I'd advise you to exercise caution when doing this - certainly you will want to be vigilant with regard to altering your data, retain a copy of your raw data while a do file manipulates the data in memory, etc.
in my case, i have an expression transformation which uses the default function ERROR('transformation') to skip the records in which date value coming inside is not in the correct format. In this, the skipped rows are not written to the reject files, so that we are getting the reconcilation problem. I need the skipped rows to be written to the bad files.Please help me how can i achieve this.
Put the Update Strategy transformation in your mapping and flag these rows for reject (use the DD_REJECT constant).
More information: Update Strategy Transformation
Well, don't use the abort() function then. Use a router to write the bad formated dates to a different target then.
We’re using JCo 3.0 to connect to RFCs and read data from SAP R/3. We use one RFC RFC_READ_TABLE often and use a second custom RFC to read employee information. My questions revolve around a third RFC RSAQ_REMOTE_QUERY_CALL. I'm calling an ad-hoc query I built in SAP using this RFC but I’m not getting the expected results. The main problem is that it appears that SAP is ignoring one of my selection criteria and using what was saved in SAP when I originally built it. The date criterion stored in my ad-hoc is 6/23/2013. If I pass in 6/28/2013 from JCo, I get the same results as if I had passed 6/23/2013 from JCo.
We have built several ad-hoc queries whose only criteria is a personnel number and call them successfully using RFC RSAQ_REMOTE_QUERY_CALL.
Background on my ad-hoc query: reporting period of today, joining together four aspects of an employee’s information: their latest action (hire, rehire, etc.), organization (e.g. company), pay (e.g. pay scale level) and communication (e.g. email). The query will run every workday.
Here are my questions:
My ad-hoc has three selection criteria. The first two are simple strings. The third is a date. The date will vary each time the query runs. We are referencing the first criteria using SP$00001, the second with SP$00002 and the third with SP$00003. The order of the criteria changes from the ad-hoc to SQ01 (what was SP$00001 in the ad-hoc is now SP$00003). Shouldn’t we reference them in the order defined in the ad-hoc (e.g. SP$00001)?
The two simple string selections are using OPTION “EQ”. The date criteria is using OPTION GT (greater than). Is “GT” correct?
We have some limited accessibility to SAP. Is there a way to see which SP$ parameters are mapped to which criteria?
If my ad-hoc was saved with five criteria but four of them never change when I call the ad-hoc from JCo, do I just need to set the value of the one or do I need to set the other four as well?
Do I have to call this ad-hoc using a variant (function.getImportParameterList().setValue(“VARIANT”, “VARIANT_NAME”))?
Does the Reporting Period have an impact on the date criteria? I have tried changing the Reporting Period to be PNPBEGDA = today and PNPENDDA = today and noticed no change.
Is there a way in SAP to get a “declaration” of your ad-hoc (name, inputs, outputs, criteria)? I have looked at JCoFunction.toXml() and JCoFunctionTemplate. These are good if you want to see something at runtime before it goes to SAP, but I’m looking for something I can use on the JCo end to help me write Java code that matches the ad-hoc.
I have looked at length on the web for answers to my questions and have not found anything that is useful. If there is anything which would help me, please let me know.
Thanks,
LM
Since I don't know much about SQnn, I won't be able to answer all of your questions...
I don't know, sorry.
It should be, at least it's the usual operator for greater than.
Yes - set an external breakpoint right inside the function module and trace its execution while performing the RFC call. Warning: At least basic ABAP knowledge required.
I don't know, sorry.
I don't know either, sorry.
That would depend on the query, I suspect...
JCo won't be able to help you out there - it doesn't know about queries, it only knows function modules. There might be other RSAQ_* function modules to get that information though.
I played with setting up a variant in SQ01 for my query. I added some settings in the variant that solved my problem and answered several of my questions in my post. The main thing I did was add a dynamically calculated date as part of my criteria. Here's how:
1. In SQ01, access menu "Go To" -> "Maintain Variants".
2. Choose your variant and in subobjects, choose "Attributes" and click "Change".
3. In the displayed list, find your date criterion.
4. Choose "D" in Selection Variable, choose a comparison option (mine was GT for greater than), and a "Name of a Variable" (really, this is the type of dynamic date calculation you need).
5. Go back to the Subobjects panel, choose "Values" and click "Change".
6. Enter any other criteria you need in the "Program selections" section.
7. Save the variant.
By doing this, I don't need to pass anything into the query from JCo. Also, SAP will automatically update the date criteria you entered in step #4 above.
So to to answer my questions from my original post:
1 and 4. It doesn't matter because I'm no longer passing anything in from JCo.
2. "GT" is Greater Than.
3 and 7. If anyone knows, I'd really like to find out.
5. Use the name you as it is in SAP (step #2 above).
6. I still don't know, but it's not holding me up.
I'm posting this in case anyone out there needs this type of information. Thanks to Esti and vwegert for helping me out.