ASP Type mismatch error with SELECT...FOR UPDATE statement

[Steve]

ASP error number 13 - Type mismatch with SELECT...FOR UPDATE statement

I got ASP error number 13 when I use the SELECT...FOR UPDATE statement
as below.
However, if I use SELECT statement without FOR UPDATE, it is fine and
no error.
I also tried Set objRs = objConn.Execute("SELECT * FROM EMP UPDATE OF
EMPNO"), but it still couldn't help.

any ideas? I tried to search in the web but couldn't find similar
problem. Is it because
the setting problems?


Here's the code fragment:
========================
On Error Resume Next
Set objConn = Server.CreateObject("ADODB.Connection")
objConn.Open strConnectionString
Set objRs = Server.CreateObject("ADODB.RecordSet")
objRs.CursorLocation = adUseClient
objRs.open "SELECT * FROM EMP UPDATE OF EMPNO", objConn,
adOpenForwardOnly, adLockBatchOptimistic
//etc...
ErrHndl:
response.write Err.Source & "<br>"
response.write "Error number " & err.number & "<br>"
response.write "Error description " & err.description & "<br>"
response.end


Errors:
=======================
Microsoft VBScript runtime error
Error number 13
Error description Type mismatch


Please advise. thanks a lot!!

 

[Bob Lehmann]

Where are you getting this syntax from - 'update of', 'select for update'?

Bob Lehmann

 

[Bob Barrows [MVP]]

ASP error number 13 - Type mismatch with SELECT...FOR UPDATE statement

Never ask a database-related question without revealing what database type
and version you are using.

I have never seen "FOR UPDATE" used except in SQL Server. In SQL Server, it
can only be used when declaring a T-SQL cursor. So, even in SQL Server, if
you use it anywhere else, you will get a syntax error.

I cannot speak for other databases like Oracle.

Why do you wish to (or think you need to) use this syntax?

Bob Barrows

 

[Steve]

I am using oracle 9i database. I tried to execute the query in Oracle
and it works fine, then it should work fine if the ASP page executes
that query runs on Oracle?

 

[Bob Barrows [MVP]]

I don't know. I have no experience with Oracle.
What is the purpose of that syntax in Oracle? I.E., what is the goal you
are trying to accomplish that can't be accomplished with standard ANSI
SQL?

Bob Barrows

 

[Steve]

I tried to put con.BeginTrans and it seems working. Is that all I
need??

objConn.BeginTrans
objRS.Open "SELECT * FROM EMP UPDATE OF EMPNO", objConn,
adOpenForwardOnly, adLockBatchOptimistic
con.CommitTrans

 

[Steve]

The interesting thing is that why we need to call objConn.BeginTrans if
we use UPDATE OF clause? For other regular SQL statement, we don't need
to call objConn.BeginTrans at all, and I never use this method before.
Is this ASP specific problem?

please advise. thanks again!!

 

[Steve]

Basically below is what I am doing, and the interesting observation is
that Oracle SELECT ... FOR UPDATE clause needs to use with
objConn.BeginTrans method. I still don't understand what is the reason.
Any ideas?

Another concern is do you think it is possible another transaction can
happen right after objConn.RollbackTrans (after step 1 & 2), since the
lock has released? If this is the case, then current_balance may not be
updated when the application calls tb_update() and tb_insert() methods.


Pseudocode
==========
//1) call get_balance() method to perform select statement to get
current_balance
//some transaction happens here ????
//2) call tb_update() method to perform update statement based on
current_balance
//some transaction happens here ????
//3) call tb_insert() method to perform insert statement based on
current_balance

code fragment of get_balance() method:
=====================================
objConn.BeginTrans
objRS.Open "SELECT * FROM EMP FOR UPDATE OF EMPNO", objConn,
adOpenForwardOnly, adLockBatchOptimistic
current_balance = objRS(0)
objConn.RollbackTrans



Please advise more. thanks!!!

 

[Bob Barrows [MVP]]

More details please. It appears that you are planning to write some sort of
procedural code to do something that can be done in a single efficient
set-based operation.

I'm still not clear what the FOR UPDATE clause does for you in Oracle.

 

[Bob Barrows [MVP]]

On reflection, I think you may get quicker, more focussed help if you find
an Oracle newsgroup or forum and post your scenario there. They will
probably be more able to tell you the most efficient way to accomplish your
task than we would.

This really sounds like the type of activity I would be doing via a stored
procedure.

Bob Barrows

 

[Anthony Jones]

Basically below is what I am doing, and the interesting observation is
that Oracle SELECT ... FOR UPDATE clause needs to use with
objConn.BeginTrans method. I still don't understand what is the reason.
Any ideas?

Another concern is do you think it is possible another transaction can
happen right after objConn.RollbackTrans (after step 1 & 2), since the
lock has released? If this is the case, then current_balance may not be
updated when the application calls tb_update() and tb_insert() methods.


Pseudocode
==========
//1) call get_balance() method to perform select statement to get
current_balance
//some transaction happens here ????
//2) call tb_update() method to perform update statement based on
current_balance
//some transaction happens here ????
//3) call tb_insert() method to perform insert statement based on
current_balance

code fragment of get_balance() method:
=====================================
objConn.BeginTrans
objRS.Open "SELECT * FROM EMP FOR UPDATE OF EMPNO", objConn,
adOpenForwardOnly, adLockBatchOptimistic
current_balance = objRS(0)
objConn.RollbackTrans



Please advise more. thanks!!!

FOR UPDATE informs Oracle that the rows in the selected set are about to be
updated. It therefore will place a lock on them. For that lock to have any
meaning it needs to be made in the context of a transaction.

The if you use the RollbackTrans call as it seems you are in the code above
you might as well not bother with the transaction at all and drop the FOR
UPDATE clause.

The sequence you've outlined above should be protected by a transaction. It
would be best handled by an SP in ORACLE that does all the transaction
management locally. If you must do it in ASP then you need a
BeginTrans/CommitTrans to span the whole sequence.


Bob, FOR UPDATE is the same as using the table hint SERIALIZABLE in SQL
Server.

 

[Bob Barrows [MVP]]

FOR UPDATE informs Oracle that the rows in the selected set are about
to be updated. It therefore will place a lock on them. For that
lock to have any meaning it needs to be made in the context of a
transaction.

The if you use the RollbackTrans call as it seems you are in the code
above you might as well not bother with the transaction at all and
drop the FOR UPDATE clause.

The sequence you've outlined above should be protected by a
transaction. It would be best handled by an SP in ORACLE that does
all the transaction management locally. If you must do it in ASP
then you need a BeginTrans/CommitTrans to span the whole sequence.


Bob, FOR UPDATE is the same as using the table hint SERIALIZABLE in
SQL Server.

Ah, that turns the light on! Thanks.

Still, it seems to me that a set-based rather than cursor-based solution
should be pursued for this.

 

[Steve]

Anthony:

I will use ASP approach without using stored procedure. What bothers me
is that there are 3 methods that perform 3 different transactions. Do
you suggest I should put all 3 different transactions into a single
method?

In get_balance() method, I put SELECT...FOR UPDATE statement inside
BeginTrans/RollbackTrans block instead of BeginTrans/CommitTrans, since
I think it just tries to lock the row and no updates happen in that
get_balance() method. However, there will be table updates in
tb_update() and tb_insert() methods. It seems to me that ASP requires
BeginTrans method in order to use SELECT...FOR UPDATE statement, but I
have no idea why. My understanding is that BeginTrans will open a
nested transaction, but what is the rationale behind that?

Another concern is that if I continue to use 3 separate methods, is it
possible to have transactions happen in between method calls?

Again, pleae advise more and thanks for your suggestions and inputs.

Steve.

 

[Steven Burn]

Last time I checked, "UPDATE FOR ..." was not a valid statement in an SQL
string .... it should instead be;

sSQL = "UPDATE [TABLE_NAME] SET FIELD1 = '" & New_Value & "' etc
etc........."

Not quite sure where the BeginTrans/RollbackTrans etc comes from as I've
never heard of them myself ......... but thats just me....

As an additional FYI ..... you should NEVER EVER EVER EVER use "Select *"

http://aspfaq.com/show.asp?id=2096

But the experts know best so I shall retire back to my lil' corner ........

--
Regards

Steven Burn
Ur I.T. Mate Group
www.it-mate.co.uk

Keeping it FREE!

 

[Bob Lehmann]

'UPDATE FOR' is an Oracle DB statement. Apparently, it locks rows that are
being updated.

Bob Lehmann

Last time I checked, "UPDATE FOR ..." was not a valid statement in an SQL
string .... it should instead be;

sSQL = "UPDATE [TABLE_NAME] SET FIELD1 = '" & New_Value & "' etc
etc........."

Not quite sure where the BeginTrans/RollbackTrans etc comes from as I've
never heard of them myself ......... but thats just me....

As an additional FYI ..... you should NEVER EVER EVER EVER use "Select *"

http://aspfaq.com/show.asp?id=2096

But the experts know best so I shall retire back to my lil' corner .........

--
Regards

Steven Burn
Ur I.T. Mate Group
www.it-mate.co.uk

Keeping it FREE!

Anthony:

I will use ASP approach without using stored procedure. What bothers me
is that there are 3 methods that perform 3 different transactions. Do
you suggest I should put all 3 different transactions into a single
method?

In get_balance() method, I put SELECT...FOR UPDATE statement inside
BeginTrans/RollbackTrans block instead of BeginTrans/CommitTrans, since
I think it just tries to lock the row and no updates happen in that
get_balance() method. However, there will be table updates in
tb_update() and tb_insert() methods. It seems to me that ASP requires
BeginTrans method in order to use SELECT...FOR UPDATE statement, but I
have no idea why. My understanding is that BeginTrans will open a
nested transaction, but what is the rationale behind that?

Another concern is that if I continue to use 3 separate methods, is it
possible to have transactions happen in between method calls?


Again, pleae advise more and thanks for your suggestions and inputs.

Steve.

to

be

have

any

transaction.

It

 

[Anthony Jones]

Anthony:

I will use ASP approach without using stored procedure. What bothers me
is that there are 3 methods that perform 3 different transactions. Do
you suggest I should put all 3 different transactions into a single
method?

In get_balance() method, I put SELECT...FOR UPDATE statement inside
BeginTrans/RollbackTrans block instead of BeginTrans/CommitTrans, since
I think it just tries to lock the row and no updates happen in that
get_balance() method. However, there will be table updates in
tb_update() and tb_insert() methods. It seems to me that ASP requires
BeginTrans method in order to use SELECT...FOR UPDATE statement, but I
have no idea why. My understanding is that BeginTrans will open a
nested transaction, but what is the rationale behind that?

Where's the nested transaction? Without a specific BeginTrans command the
only transaction is an implicit one that a DB engine may choose to create
fleetingly during the operation a single command.

In order to bind a series of commands under a transaction such a transaction
needs to be explicitly declared. Are you saying you are already doing that?
If so you should remember that a transaction is created with in the scope of
a connection so the same connection should be used for all commands that are
to operate under that transaction

Another concern is that if I continue to use 3 separate methods, is it
possible to have transactions happen in between method calls?

Without the protection of an explicit transaction declared before calling
these methods then yes. The whole point of FOR UPDATE is to lock a set of
rows so that don't change while modifications are being made. However a DB
Lock needs to be created in the context of an explicit transaction.

IMO this design is flawed. You should have a single method to update a
balance or whatever which in turn calls an SP that makes the change for you.
The SP should use ORACLEs native commands to create a transaction perform
the updates (and as Bob pointed out you probably don't even need the SELECT
to do this) and then commit the transaction.

 

[Steven Burn]

hehe prolly why I've never heard of it (don't use Oracle, lol).

Cheers for the correction ;o)

--
Regards

Steven Burn
Ur I.T. Mate Group
www.it-mate.co.uk

Keeping it FREE!

'UPDATE FOR' is an Oracle DB statement. Apparently, it locks rows that are
being updated.

Bob Lehmann

Last time I checked, "UPDATE FOR ..." was not a valid statement in an SQL
string .... it should instead be;

sSQL = "UPDATE [TABLE_NAME] SET FIELD1 = '" & New_Value & "' etc
etc........."

Not quite sure where the BeginTrans/RollbackTrans etc comes from as I've
never heard of them myself ......... but thats just me....

As an additional FYI ..... you should NEVER EVER EVER EVER use "Select *"

http://aspfaq.com/show.asp?id=2096

But the experts know best so I shall retire back to my lil' corner ........

--
Regards

Steven Burn
Ur I.T. Mate Group
www.it-mate.co.uk

Keeping it FREE!

Anthony:

I will use ASP approach without using stored procedure. What bothers me
is that there are 3 methods that perform 3 different transactions. Do
you suggest I should put all 3 different transactions into a single
method?

In get_balance() method, I put SELECT...FOR UPDATE statement inside
BeginTrans/RollbackTrans block instead of BeginTrans/CommitTrans, since
I think it just tries to lock the row and no updates happen in that
get_balance() method. However, there will be table updates in
tb_update() and tb_insert() methods. It seems to me that ASP requires
BeginTrans method in order to use SELECT...FOR UPDATE statement, but I
have no idea why. My understanding is that BeginTrans will open a
nested transaction, but what is the rationale behind that?

Another concern is that if I continue to use 3 separate methods, is it
possible to have transactions happen in between method calls?

Pseudocode
==========
//1) call get_balance() method to perform select statement to get
current_balance
//some transaction happens here ????
//2) call tb_update() method to perform update statement based on
current_balance
//some transaction happens here ????
//3) call tb_insert() method to perform insert statement based on
current_balance

code fragment of get_balance() method:
=====================================
objConn.BeginTrans
objRS.Open "SELECT * FROM EMP FOR UPDATE OF EMPNO", objConn,
adOpenForwardOnly, adLockBatchOptimistic
current_balance = objRS(0)
objConn.RollbackTrans

Again, pleae advise more and thanks for your suggestions and inputs.

Steve.


Anthony Jones wrote:
Basically below is what I am doing, and the interesting

observation

is not
be

about

to have code
above the
FOR transaction.