Difference between NULL and two single quotes

Hi,
Please advice me on the following.
First let's do an update.
update table_name set column_name ='';
After updating why do following queries return different results?
1. select count(*) from table_name where column_name is null;
2. select count(*) from table_name where column_name ='';
I understand update query set the column values to null and first select statement is the correct way to get the number of null values. But I want to know what's wrong with the second select statement.
Thank You.
Edited by: Sajeeva Lakmal on Jan 15, 2013 9:29 PM

Sajeeva Lakmal wrote:
Hi,
Please advice me on the following.
First let's do an update.
update table_name set column_name ='';
After updating why do following queries return different results?
1. select count(*) from table_name where column_name is null;
2. select count(*) from table_name where column_name ='';
I understand update query set the column values to null and first select statement is the correct way to get the number of null values. But I want to know what's wrong with the second select statement.
Thank You.
Edited by: Sajeeva Lakmal on Jan 15, 2013 9:29 PMhow can I reproduce what you report?

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Hi All,
Is the below right?
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user605246 wrote:
Hi All,
Is the below right?
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Regards,
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Hi,
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command-double-click is your friend
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JavaProwler wrote:
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Message was edited by: Aleksey Kuznetsov

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corlettk wrote:
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Girish,
I wont say that I am correcting you as this is like that half glass full/empty thing.May be what I see is half empty , you would see the same as half full.
Well now coming to the explanation.I am saying honestly , I got more confused after reading your definitions.What do you mean by saing that tablespace is not virtual.I see it as purely virtual.We don't say it as virtual tablespace or logical tablespace but it is actualy logical/virtual, having no existance but just the definition right?
How can you say that the size of virtual is larger than logcial?The size of tablespace is actualy the sum total of size of datafiles.So it actualy becomes very larger right?Much larger than JVM which is of few megs only.
The point 3 totally knocked me out.I have no idea what you said.
Ok I tell you this.Just remember the definition that Hans gave already.If you ask me than its the best definition that we can have. Just remember this and if some one asks you more further than give them your point 3 definition and tell them understand this ;-).Please don'tmind I am just kidding. Its just semantics.Don't get lost into it.You will find many people using both the terms interchangibly. So its ok.I shall stick with Hans's defintion,simple and concise.There are lot more other topics to dig upon in oracle.I can mail you lots of them.Spend time on those.Don't think that I am demotivating you.I understand you asked only because you have a doubt.But we got a good resolution of it and beyond that, its not of much use to dig it atleast not in the technial terms.
Cheers
Aman....
PS:Are you on oraclecommunity.net?

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Hi,
i want to know difference between BAPI and RFC in SAP,
can we call SAP GUI screen from NON SAP System Using BAPI.
Reg,
Hariharan

Hi Ravishankar,
The difference is not importat while you understand the concept.
I think, RFC is the protocol for calling functions from external systems in R/3.
I understand like BAPI a series of complet functions that SAP offers you for use and model a business use.
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A remote function call is a call to a function module running in a system different from the caller's. The remote function can also be called from within the same system (as a remote call).
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BAPI
BAPIs are standardized programming interfaces (methods) enabling external applications to access business processes and data in the R/3 System.
BAPIs provide stable and standardized methods to achieve seamless integration between the R/3 System and external applications, legacy systems and add-ons.
BAPIs are defined in the BOR(Business object repository) as methods of SAP business object types that carry out specific business functions.
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Reading instances of SAP business objects
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Create( ) and CreateFromData! ( )
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Change( )
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Delete( ) and Undelete( ) The BAPI Delete() deletes an instance of an SAP business object type from the database or sets a deletion flag.
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Cancel ( ) Unlike the BAPI Delete(), the BAPI Cancel() cancels an instance of a business object type. The instance to be cancelled remains in the database and an additional instance is created and this is the one that is actually canceled. The Cancel() BAPI is an instance method.
Add<subobject> ( ) and Remove<subobject> ( ) The BAPI Add<subobject> adds a subobject to an existing object inst! ance and the BAPI and Remove<subobject> removes a subobject from an object instance. These BAPIs are instance methods.
Check these Links out
http://searchsap.techtarget.com/ateQuestionNResponse/0,289625,sid21_cid558752_tax293481,00.html
http://www.sap-img.com/abap/interview-question-on-bapi-rfc-abap-objects-tables.htm
http://www.sap-img.com/fu033.htm
http://www.sap-img.com/abap/ale-bapi.htm
Refer following SDN threads:
Diff. Between BAPI and RFC
Re: BAPI and RFC
Hope this resolves your query.
Reward all the helpful answers.
Regards

Difference between NULL and two single quotes

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