Date Conversion Through User Defined Function

hi,
I am trying to convert the SAP Date format i.e. yyyymmdd to dd/mm/yyyy date format by using a custom Function.
the code is.:
public String ConvertDate(String dateSAP,Container container){
String inputdate= dateSAP;
int month=Integer.parseInt(inputdate.substring(4,6));
int date=Integer.parseInt(inputdate.substring(6,inputdate.length()));
int year=Integer.parseInt(inputdate.substring(0,6));
return (date"/"month"/"year);
but i get an error:
RuntimeException in Message-Mapping transformation: Runtime exception during processing target field mapping /ns0:MT_IB_Project_Master_TAG/statement2/Tablename/access/PLANNED_END_DATE. The message is: Unparseable date: "20070103"
what do i need to change in this code
Regards,
Tarun

String smonth=dateSAP.substring(4,6);
String sdate=dateSAP.substring(6,8);
String syear=dateSAP.substring(0,4);
return (sdate""smonth""syear);
where dateSAP is my importing parameter

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User defined function to find difference between dates

format of dtActivityStartDate/dtActivityFinishDate: 2010-09-17 14:50:51.150
usdFuncTimeCalc (vcActivityName,dtActivityStartDate, dtActivityFinishDate) -- user defined function
i need to calculate time elapsed for that type of activity following are the rules:
(If Process Request is the activity)
Working Days: Monday through Saturday
Hours of Operation: 9AM – 5PM
only working hours of day need to the counted like for example if it is sep 15 11 Am is dtActivityStartDate & Sep 17 is dtActivityFinishDate is 10 Am. then time elapsed is 11am to 5pm on sep 15 , 9 to 5 on sep 16 & 9 to 10 on sep 17 so total should be
6+ 8 + 1 = 15 hours + minutes.
format of date time: 2010-09-17 14:50:51.150
vcActivityName = Process Request
Don't worry about process request...

I hv modified the code to make it more generic inorder to suit any timings (customizable) from Monday - Saturday.
declare
-- ** b u s i n e s s _ h o u r s **
-- business_hours returns the number of work houts (9 am through 5 pm,
-- Monday through Saturday) between in_start_dt and in_end_dt.
-- If in_start_dt > in_end_dt, the results will be <= 0.
-- Holidays are not considered.
in_start_dt DATE := to_date('15-SEP-2010 11:00:00','DD-MON-RRRR HH24:MI:SS');
in_end_dt   DATE := to_date('17-SEP-2010 10:00:00','DD-MON-RRRR HH24:MI:SS');
d          NUMBER; -- Hours of either start_dt or end_dt after midnight
end_dt     DATE := GREATEST(in_start_dt, in_end_dt); -- In case dates were in wrong order
return_val NUMBER; -- Total number of working hours
start_dt   DATE := LEAST(in_start_dt, in_end_dt); -- In case dates were in wrong order
start_time number := 9;
end_time   number := 17;
BEGIN
WITH all_days AS(
    SELECT start_dt + LEVEL - 1 AS a_dt
      FROM dual
    CONNECT BY LEVEL <= 1 + TRUNC(end_dt) - TRUNC(start_dt))
      --SELECT SUM(12)
       SELECT SUM(end_time-start_time)
        INTO return_val
        FROM all_days
       WHERE TO_CHAR(a_dt,'Dy','NLS_DATE_LANGUAGE = ''ENGLISH''') NOT IN ('Sun');
dbms_output.put_line('Return_Val_1 : '||return_val);
-- Adjust hours from start_dt, if necessary
IF TO_CHAR(start_dt, 'Dy', 'NLS_DATE_LANGUAGE = ''ENGLISH''') NOT IN ('Sun') THEN
     -- Calculate nbr of hours passed from midnight
     d := 24 * (start_dt - TRUNC(start_dt));
     dbms_output.put_line('d:'||d);
     IF d >= end_time THEN -- d has passed 5 PM (end_time)
        -- Don't count start_dt if it has passed the closing hours
        return_val := return_val - (end_time-start_time);
        dbms_output.put_line('if-d:'||return_val);
     ELSIF d > start_time and d < end_time THEN -- d has passed 9 AM but less than 5 PM
        -- Don't count the part of start_dt which has passed the opening hours
        return_val := return_val - (d - start_time);
        dbms_output.put_line('else-d:'||return_val);
     END IF;
END IF;
dbms_output.put_line('');
dbms_output.put_line('Return_Val_2 : '||return_val);
-- Adjust hours from end_dt, if necessary
IF TO_CHAR(end_dt, 'Dy', 'NLS_DATE_LANGUAGE = ''ENGLISH''') NOT IN ('Sun') THEN
     d := 24 * (end_dt - TRUNC(end_dt));
     dbms_output.put_line('d:'||d);
    IF d <= 9 THEN -- d < 9 AM
       -- Don't count end_dt itself
       return_val := return_val - (end_time-start_time);
       dbms_output.put_line('if-d:'||return_val);
    ELSIF d > start_time and d < end_time THEN -- d > 5 PM
      -- Don't count part of end_dt
      return_val := return_val - (end_time - d);
      dbms_output.put_line('else-d:'||return_val);
    END IF;
END IF;
dbms_output.put_line('');
dbms_output.put_line('Return_Val_3 : '||return_val);
IF in_start_dt > in_end_dt THEN
      return_val := -return_val;
END IF;
dbms_output.put_line('');
dbms_output.put_line('Return_Val_4 : '||return_val);
END;Plz note the following points of the code :
1) You'll need to convert it a function, I just made it a declare..begin..end; block.
2) I hv used the same timings for start & end as you hv mentioned.
3) The 2 variables "start_time" and "end_time" take the opening & closing business hours respectively in a 24 hour format.
4) You might want to remove the DBMS_OUTPUT ... stmts which I had added for debugging.
It was an interesting code block to analyze ... :-)

Calling user defined functions through OBIEE

Can anyone tell me how I can call the user defined functions on database through the new BI tool.
The idea is to collect certain parameters through the prompt when launching the request, the function is supposed to pick up the parameters, make a certain calculation, and return a value.
I wrote the function, I just need help over how to call the function through the BI tool - that was pretty easy in the old Discoverer.
Thanks.
Message was edited by:
user611377

Hi Kresimir ,
You can use EVALUATE function to call a user defined function.
EVALUATE('FUNCTIONNAME(%1,..)' As DATATYPE,parameter1,...)
Here DATATYPE is the returntype of function.
Hope this will help.
Thanks
Ashok

UDF(user defined function) for standard date transformate function,

Hi All,
Hope you are doing good !!!
I have a requirement where i need to write an UDF(user defined function). Please help me in writing the code for below logic-
I am getting my Input as 111213 where 11 denotes HH 12 denotes mm 13 denotes ss. I need ti insert : between hh:mm:ss
Please help me achieving a code for below logic
I have used standard date transformate function, there i am getting spaces as separator in my input resulting an errors i am sending without spaces.
Regards,
Vijay Kumar.

Hello,
I am getting my Input as 111213 where 11 denotes HH 12 denotes mm 13 denotes ss. I need ti insert : between hh:mm:ss
Please help me achieving a code for below logic
I have used standard date transformate function, there i am getting spaces as separator in my input resulting an errors i am sending without spaces.
What do you mean by spaces? Can you try the mapping below?
inputDate -> replaceString -> dateTrans(inputDateFormat: HHmmss outputDateFormat: HH:mm:ss) -> target
Constant: -> /
Constant:-> /
Hope this helps,
Mark

User defined function in where IN clause

Hi,
I have a Function who returns in priview:
(1,2,3,4)
Now i am using this function in SQL where clause
Select from debug where id in debug.debug_process()
On execute select i am getiing ORA-01722 invalid number , i understand that functions return not only numbers but character symbols too '(,)'
Are it posible to use user defined function who do not return NUMBER in Where clause IN statement ? If not what tips can sugest me for getting list of values for use in IN Clause?
ID.
Thanks!

Hi,
Please try:
You can use SYS REFCURSOR for return your data.
create or replace function get_debug return sys_refcursor is
     v_rc sys_refcursor;
   begin
     open v_rc for 'select * from debug where id in '|| debug.debug_process();
     return v_rc;
   end;
Function created.
Now, if we look at using this through SQL*Plus we first create ourselves a ref cursor variable to accept the results of the function, and then call the function to get the ref cursor back..
SQL> var rc refcursor
SQL> exec :rc := get_debug ;
SQL> print rc;
Regards
Mahir M. Quluzade

Help in Mapping: User defined function

Hi All, I need your help in doing the following mapping:
The source contains the below fields:
Source_MT -- Under this          1...1
   LineItem                                 1...Unbounded
     CompanyCode          1..1
     Amount               1..1
   SubTotal                               1...Unbounded
     CompanyCode          1...1
     Amount               1...1
And the Target strunture should be:
Target_MT -- Under this
   Target                               1...unbounded
     CompanyCode          1...1
     AmountMatched          1...1
There will be multiple line items in the source for each compony code which I need to loop through and add the amounts. For a company code, The sum of the amounts in the line items should match with the amount in the Subtotal/Amount.
For each company code, a target should be created with the result whther the amounts were matched or not.
Below is the data example:
Source:
Line Item :
     CompanyCode          Amount
     ABC               5
     ABC               5
     XYZ               10
     ABC               7
     XYZ               6
Sub Total :
     CompanyCode          Amount
     ABC               17
     XYZ               5
Target should be:
CompanyCOde          Amount
ABC               Matched
XYZ               Not Matched
Hope I am clear with my requirement. Please let me know if you need more clarity.
I was able to create mapping, if the line items contains single company code. Need help with multiple company codes.
Any help would be appreciated.
Edited by: GP on Jan 29, 2008 5:55 PM
Edited by: GP on Jan 29, 2008 5:57 PM

I am still working on the same map (please refer above) for which you gave th3e solution. The solution almost worked.
I need to validate the line items with the subtotals. If the validation fails, I should throw an custom exception. If the validation is successful, then do nothing (do not create the target element).
Hope I am clear. Please let me know if I am not clear.
LineItem1: 10
LineItem2: 20
SubTotal1: 30
LineItem3: 5
LineItem4: 5
SubTotal2: 15
In the above example, eventhough LineItem1 and LineItem2 sum up to Subtotal1, LineItem3 and LineItem4 doesn't sum up to SubTotal2. So it should throw an exception because second validation failed.
Also, it should not create target element because first validation was successful.
I used the logic int he below link :
[http://www.flickr.com/photo_zoom.gne?id=2229287904&size=o]
In the "else" part of "If else" statement, I have a user defined function which throws exception.
If the output is "true", I am avoiding creating the target element using "Createif" statement.
But strangely, when the vaildation of first set fails (LineItem1, LineItem2 and Subtotal1), then it is throwing the exception.
But when the validation of second set fails, then it is not throwing the exception.
My current map looks like below:
[http://www.flickr.com/photos/23389577@N02/2234471441/sizes/l/]
Edited by: GP on Feb 1, 2008 6:46 PM
Edited by: GP on Feb 1, 2008 6:50 PM
Edited by: GP on Feb 1, 2008 7:01 PM

Whether i would write user-defined function convert euro into rupee or USD

hi expects,
whether it need to right user defined functions for convert the currency into euro or any other currency into rupee or USD.as my client is having business in different region.please help me.
Edited by: santosh kumar sethis on Apr 24, 2008 10:39 AM

I suggest to use a UDF and call an RFC function\BAPI in the ERP system.
Currency conversion values are maintained in the ERP system by the Financial people so you'll have the most updated rates.(maybe even according to the date of purchase)
So 3 scenarios come to mind:
1. if the message is send from a 3rd party system or from ERP ,the currency must be converted already in the message,
2.the RFC of the ERP will do the conversion or you.
3.Find a currency conversion web service that has parameters of date and currency so you'll do the conversion as accurate as possible.
bare in mind:
there might be inconsistency of the money values due to the change in currency from the time the order was placed in the system till the time of entering the SAP .ask for the advise of a financial person so you wont do any mistakes in conversion.
ANY WAY - don't use hard coded constants in XI mapping for currency conversion.
Good luck.
Nimrod

How many types of user defined functions are there?

how many types of user defined functions are there?

Hi Ramakrishna,
A user-defined function is only visible in the message mapping in which you created it. You can insert the function in the data-flow editor as a standard function by using the User-Defined function category.
You can use the following user-defined functions:
1.Simple functions, which can process individual field input values for each function call. Simple functions therefore expect strings as input values and return a string.
2.Advanced functions, which can process several field input values for each function call. You can import either all field values of a context or the whole queue for the field in an array before calling the function. For more information, see Advanced User-Defined Functions.
    go through :
http://help.sap.com/saphelp_erp2004/helpdata/en/22/e127f28b572243b4324879c6bf05a0/content.htm
     Advanced user-defined functions, which can process more than just individual field values.Instead, you can import a complete context or an entire queue for a field as an array before your function is called
    go through :
http://help.sap.com/saphelp_erp2004/helpdata/en/f8/2857cbc374da48993c8eb7d3c8c87a/content.htm
*Pls: Reward points if helpful*
Regards,
Jyoti

Converting db2 user defined functions to oracle .

Hi gurus
this is a user defined function for getting current timestamp for a null value how to do this in oracle .i am getting a problem at the input values.can anyone suggest me the changes to convert it into oracle udfs.
drop function Get_DateId()
CREATE FUNCTION Get_DateId()
RETURNS BIGINT
BEGIN ATOMIC
DECLARE      R BIGINT;
DECLARE      v_Day CHAR(2);
DECLARE      v_Month CHAR(2);
DECLARE      v_Year CHAR(4);
     SET V_Day     = SUBSTR( DIGITS (DAY(CURRENT DATE)),9);
     SET V_Month     = SUBSTR( DIGITS (MONTH(CURRENT DATE)),9);
     SET V_Year     = RTRIM(CHAR(YEAR(CURRENT DATE)));
     SET R= BIGINT(v_Year||V_Month||V_Day|| '00000000' );
RETURN R ;
END
@

You'll need to get the syntax for PL/SQL function calls right. You will need something like
create or replace function whatever( arg datatype, arg datatype...) return varchar2 is
--define any local variables here
begin
   return to_number(to_char(systimestamp,'the edit mask you want to use'));
end;
/You might do the conversion inline and dispense with the function compeletly if you're just generating a value.

Error while using user defined function in reports

Hi,
When I use the below user defined function in oracle reports I got the wrong number of arguments error
select test_function(id,a_number,v_date-14,b_number) from dual;
If I remove -14 from the argument it works. But iIneed to subtract 14 days from the date.
Thanks for your help.

select test_function(id,a_number,v_date-14,b_number) from dual;
you have to give the command like this to_date(v_date,'dd-mon-yyyy')-14
because the v_Date you choose in the parameter form is not having the corrent date format
the format dd-mon-yyyy is the format in which v_date is passed by the user.

Using a User Defined Function as a constraint within a temporary table.

Hello,
I am trying to create a temp table that uses a UDF in a constraint. I'm getting the following error message
Msg 4121, Level 16, State 1, Line 1
Cannot find either column "dbo" or the user-defined function or aggregate "dbo.CK_LoseTeamSportExists", or the name is ambiguous.
I've tested the function and it works in other contexts. Any idea? All code below:
Thanks,
- Bryon
create function dbo.CK_LoseTeamSportExists (@loseteam int, @sportid int)
returns bit
as
begin
declare @return bit
if exists
select TeamID, sportid from Link_TeamSport
where
TeamID = @loseteam
and
SportID = @sportid
set @return = 1
else set @return = 0
return @return
end
go
create table #check
SportID int
,WinTeamID int
,LoseTeamID int
,check
(dbo.CK_LoseTeamSportExists(LoseTeamID,SportID) = 1)

Please post DDL, so that people do not have to guess what the keys, constraints, Declarative Referential Integrity, data types, etc. in your schema are. Learn how to follow ISO-11179 data element naming conventions and formatting rules. Temporal data should
use ISO-8601 formats. Code should be in Standard SQL as much as possible and not local dialect.
This is minimal polite behavior on SQL forums.
>> I am trying to create a temp table that uses a UDF in a constraint. <<
You do not understand how SQL or any declarative language works!
We do not use UDFs (procedural programming)
We do not use bit flags (assembly language).
We do not use temp tables (mag tape files).
We do not use integer as identifiers (what math do you do on them?)
Your silly “Link_TeamSport” implies a pointer chain; we have no links in SQL. Where is the DDL?
Constraints are always predicates in any declarative language.
Do you know why you have to create a local variable to pass the non-relational flag back to the calling environment? FORTRAN I and II! These early languages has to use hardware registers in the first IBM computers to return results. In your ignorance, you mimic
them!
We do not use if-then-else control flow in any declarative language. We have CASE expressions that we put where you have a local variable getting an assignment.
I see you also put the comma at the start of the line. We did that with punch cards, so we could re-use them 50 years ago.
In SQL, we would use REFERENCES to assure a team reference exists. We use names for teams because they are entities, not quantities:
CREATE TABLE Game_Results
(sport_name CHAR(10) NOT NULL PRIMARY KEY,
win_team_name CHAR(12) NOT NULL
REFERENCES Teams(team_name)
ON DELETE CASCADE,
lose_team_name CHAR(12) NOT NULL
REFERENCES Teams(team_name)
ON DELETE CASCADE,
CHECK (win_team_name <> lose_team_name));
--CELKO-- Books in Celko Series for Morgan-Kaufmann Publishing: Analytics and OLAP in SQL / Data and Databases: Concepts in Practice Data / Measurements and Standards in SQL SQL for Smarties / SQL Programming Style / SQL Puzzles and Answers / Thinking
in Sets / Trees and Hierarchies in SQL

User Defined Function Missing In EF 6?

I'm using Entity Framework 6 and I have imported several user-defined functions like the one shown below, but it doesn't
appear when I try to select the function in intellisense and the model doesn't recognize this function as a method on the EF context. How do I call this function in EF 6?
<Function Name="getCycleDate" Aggregate="false" BuiltIn="false" NiladicFunction="false" IsComposable="true" ParameterTypeSemantics="AllowImplicitConversion" Schema="dbo" ReturnType="date" />
MCSD .NET developer in Dallas, Texas

Hello DallasSteve,
>> I have imported several user-defined functions like the one shown below,
What is your UDF? If it is a TVF, starting from EF5, it is supported already:
https://msdn.microsoft.com/en-us/data/hh859577.aspx
However, it is a scalar function, unfortunately, as far as I know, even entity framework 6 doesn't suport generating calls for scalar functions by default. The workaround is to write a custom method like this inside your DbContext class, for example, there
is scalar function as:
CREATE FUNCTION [dbo].[Function20150410]
@param1 int,
@param2 int
RETURNS INT
AS
BEGIN
RETURN @param1 + @param2
END
When we imported it to the model, it would generate code in SSDL as:
<Function Name="Function20150410" Aggregate="false" BuiltIn="false" NiladicFunction="false" IsComposable="true" ParameterTypeSemantics="AllowImplicitConversion" Schema="dbo" ReturnType="int">
<Parameter Name="param1" Type="int" Mode="In" />
<Parameter Name="param2" Type="int" Mode="In" />
</Function>
While, it will not generate a call method as a store produce, for a workaround, we could write a custom function as:
[DbFunction("DFDBModel.Store", "Function20150410")]
public ObjectResult<int> GetContentByIdAndCul(int id, int culture)
var objectContext = ((IObjectContextAdapter)this).ObjectContext;
var parameters = new List<ObjectParameter>();
parameters.Add(new ObjectParameter("Id", id));
parameters.Add(new ObjectParameter("Culture", culture));
return objectContext.CreateQuery<int>("DFDBModel.Store.Function20150410(@Id, @Culture)", parameters.ToArray()).Execute(MergeOption.NoTracking);
I suggest that you write this custom method a separate cs file since if we update the model, the original context call would be reset.
Calling it as:
using (DFDBEntities db=new DFDBEntities())
var result = db.GetContentByIdAndCul(1, 1).FirstOrDefault();
}s
Regards.
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User-defined function in FILTER clause

hi,
can i create the user-defined functions and use them in the FILTER clause in the sem_match function? there are some built-in functions for the FILTER clasue. however, only one function (DATATYPE(literal)) support for date/time in the built-in functions. i want to implement some user-defined funcitons in the FILTER clause which can check time intervals in ontology. there are some functions about valid time in the WorkSpace Manager such as WM_OVERLAPS, WM_CONTAINS,WM_MEETS, etc. so, can i write some functions using the these valid time functions in WM and use them in the FILTER clause? thanks a lot in advance.
hong

Hi Hong,
You don't need user-defined functions to do time interval comparisons. You can directly compare xsd:dateTime values with the built-in comparison operators: <, >, =, !=, <=, >=
For example, the query pattern below could find events that happened during event1 if we have data such as:
:event1 :startTime "2013-01-01T03:15:00Z"^^xsd:dateTime .
:event1 :endTime "2013-02-01T02:15:00Z"^^xsd:dateTime .
:event2 :startTime "2013-01-11T14:15:00Z"^^xsd:dateTime .
:event2 :startTime "2013-01-14T12:15:00Z"^^xsd:dateTime .
SELECT ?e2
WHERE
{ :event1 :startTime ?e1_st; :endTime ?e1_et .
?e2 :startTime ?e2_st; endTime ?e2_et .
FILTER (?e1_st < ?e2_st && ?e2_et < ?e1_et) }
In general, it is trivial to convert interval relations such as meets and overlaps to conditions on start and end times.
Hope this helps.
- Matt

Error in simple user defined function

Hi all,
I have seen one simple user defined function on scenario. Now it is working fine. Same code I have used another place. But it is giving some errors
D:/usr/sap/C08/DVEBMGS00/j2ee/cluster/server0/./temp/classpath_resolver/Mapc6fa0c70297511dbaf7e00c09f4504e7/source/com/sap/xi/tf/_ST_MM_.java:3: package javax.mail.internet does not exist
import com.sap.aii.mappingtool.tf3.;import com.sap.aii.mappingtool.tf3.rt.;import java.util.;import java.io.; import java.lang.reflect.;import javax.mail.internet.;import javax.mail.;import java.util.;import java.util.Date;import javax.activation.;import java.lang.reflect.;import javax.mail.event.*;
Like that it has shown 13 errors. I have given the package names in imports field what previous function has.

Hi,
Please see this from SAP help
<i>a. You can import Java packages to your methods from the Imports input field, by specifying them separated by a comma or semi-colon:
You do not need to import the packages java.lang., java.util., java.io., and java.lang.reflect. since all message mappings require these packages and therefore import them. You should be able to access standard JDK and J2EE packages of the SAP Web Application Server by simply specifying the package under Import. In other words, you do not have to import it as an archive into the Integration Repository. You can also access classes of the SAP XML Toolkit, the SAP Java Connector, and the SAP Logging Service (see also: Runtime Environment (Java-Mappings)).
In addition to the standard packages, you can also specify Java packages that you have imported as archives and that are located in the same, or in an underlying software component version as the message mapping.
b. Create your Java source text in the editor window or copy source text from another editor.</i>
http://help.sap.com/saphelp_nw04/helpdata/en/22/e127f28b572243b4324879c6bf05a0/content.htm
Regards
Vijaya

Using User Defined Function is SQL

Hi
I did the following test to see how expensive it is to use user defined functions in SQL queries, and found that it is really expensive.
Calling SQRT in SQL costs less than calling a dummy function that just returns
the parameter value; this has to do with context switchings, but how can we have
a decent performance compared to Oracle provided functions?
Any comments are welcome, specially regarding the performance of UDF in sql
and for solutions.
create or replace function f(i in number) return number is
begin
return i;
end;
declare
l_start   number;
l_elapsed number;
n number;
begin
select to_char(sysdate, 'sssssss')
    into l_start
    from dual;
for i in 1 .. 20 loop
    select max(rownum)
      into n
      from t_tdz12_a0090;
end loop;
select to_char(sysdate, 'sssssss') - l_start
    into l_elapsed
    from dual;
dbms_output.put_line('first: '||l_elapsed);
select to_char(sysdate, 'sssssss')
    into l_start
    from dual;
for i in 1 .. 20 loop
    select max(sqrt(rownum))
      into n
      from t_tdz12_a0090;
end loop;
select to_char(sysdate, 'sssssss') - l_start
    into l_elapsed
    from dual;
dbms_output.put_line('second: '||l_elapsed);
select to_char(sysdate, 'sssssss')
    into l_start
    from dual;
for i in 1 .. 20 loop
    select max(f(rownum))
      into n
      from t_tdz12_a0090;
end loop;
select to_char(sysdate, 'sssssss') - l_start
    into l_elapsed
    from dual;
dbms_output.put_line('third: '||l_elapsed);
end;
Results:
   first: 303
   second: 1051
   third: 1515
Kind regards
Taoufik

I find that inline SQL is bad for performance but
good to simplify SQL. I keep thinking that it should
be possible somehow to use a function to improve
performance but have never seen that happen.inline SQL is only bad for performance if the database design (table structure, indexes etc.) is poor or the way the SQL is written is poor.
Context switching between SQL and PL/SQL for a User defined function is definitely a way to slow down performance.
Obviously built-in Oracle functions are going to be quicker than User-defined functions because they are written into the SQL and PL/SQL engines and are optimized for the internals of those engines.
There are a few things you can do to improve function
performance, shaving microseconds off execution time.
Consider using the NOCOPY hints for your parameters
to use pointers instead of copying values. NOCOPY
is a hint rather than a directive so it may or may
not work. Optimize any SQL in the called function.
Don't do anything in loops that does not have to be
done inside a loop.Well, yes, but it's even better to keep all processing in SQL where possible and only resort to PL/SQL when absolutely necessary.
The on-line documentation has suggested that using a
DETERMINISTIC function can improve performance but I
have not been able to demonstrate this and there are
notes in Metalink suggesting that this does not
happen. My experience is that DETERMINISTIC
functions always get executed. There's supposed to
be a feature in 11g that acually caches function
return values.Deterministic functions will work well if used in conjunction with a function based index. That can improve access times when querying data on the function results.
You can use DBMS_PROFILER to get run-time statistics
for each line of your function as it is executed to
help tune it.Or code it as SQL. ;)

Date Conversion Through User Defined Function

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