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https://issues.apache.org/jira/browse/TRAFODION-2408?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=15770822#comment-15770822
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ASF GitHub Bot commented on TRAFODION-2408:
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GitHub user sandhyasun opened a pull request:
https://github.com/apache/incubator-trafodion/pull/889
[TRAFODION-2408] Changes to support "empty lob" insert/update and update
directly using lobhandle
Empty_blob()/ Emptyclob() functions will insert a dummy row into the LOB
descriptor tables as a place holder. The lobhandle will be created but will
contain no data. This lob handle can later be used to update data directly to
it without scanning the SQL table.
JIRA contains more details on syntax/examples.
You can merge this pull request into a Git repository by running:
$ git pull https://github.com/sandhyasun/incubator-trafodion empty_lob_work
Alternatively you can review and apply these changes as the patch at:
https://github.com/apache/incubator-trafodion/pull/889.patch
To close this pull request, make a commit to your master/trunk branch
with (at least) the following in the commit message:
This closes #889
----
commit 7baf325f3fd612125f49b6f6763e6e895ba52d58
Author: Sandhya Sundaresan <[email protected]>
Date: 2016-12-21T19:04:25Z
Changes to support new syntax and implementation empty_blob/empty_clob for
insert/updates
Changes to support new syntax for updating a lob directly through a
lobhandle without scanning the table.This is done via new ExeUtil operator.
Changes to add columnname info to LOBMD_ table. This helps in mapping any
given lobhandle back to the table and the column.
Added new sections to the regression test executor/TEST130 to test these
changes
commit f364d03a5b73373421b885f73302545ad5208bc7
Author: Sandhya Sundaresan <[email protected]>
Date: 2016-12-21T19:11:02Z
Merge remote branch 'origin/master' into empty_lob_work
----
> Support for empty_blob() and update syntax using lobhandle
> ----------------------------------------------------------
>
> Key: TRAFODION-2408
> URL: https://issues.apache.org/jira/browse/TRAFODION-2408
> Project: Apache Trafodion
> Issue Type: Sub-task
> Components: sql-exe
> Reporter: Sandhya Sundaresan
> Assignee: Sandhya Sundaresan
>
> This subtask in SQL is to help JDBC implementation for LOBs. They require the
> eimplementation of 2 interfaces
> .EMPTY_BLOB() , EMPTY_CLOB()
> update done directly to a lobhandle . This update syntax is different form
> the regular updates to lob columns using position.
> Assume a lob table of type :
> Create table tlob(c1 int , c2 blob, primary key (c1));
> Insert :
> Insert into tlob values (1, empty_blob());
> Insert into tlob values (1,empty_clob());
>
>
> This will create a lob handle . It will also create an empty descriptor
> handle entry and 1 chunk in the descriptor chunks table that is of size 0.
>
> The “type” of the lob handle will be the same as the underlying lob type of
> the column.
>
> Eg if we had created the table to hold external lobs
> Create table tlob(c1 int , c2 blob storage ‘external’ , primary key
> (c1));
> Insert into tlob values (1, empty_blob());
>
> The lob handle for this tlobext will contain the type ‘8’ instead of ‘2’ (as
> is the case for tlob.)
>
> But looking at the lob handle you will not be able to say if it’s empty or
> not. But if lob data is selected out it will be empty.
>
> Update:
> Assume tlob has some lob data in it.
>
> Update tlob set c2=empty_blob();
> This will replace all lob data in the table with the empty lob.
> The lob handle remains the same as before.
>
> Update tlob set c2 = stringtolob(‘xxxx’);
> This will replace the empty lob entry inth
> descriptor handle and descriptor chunks table with a new entry.
> OR
> Update tlob set c2 – stringtolob(‘xxxx’, append);
> This will append the new data to the empty lob. So
> it will leave 2 entries in the descriptor handle and descriptor chunks table.
>
> But the result when you select the data will be the same in both cases
> above.
>
>
> Update directly using a lobhandle using a buffer programmatically :
> New syntax has been introduced to allow updating a lob entry using lob
> handle directory. This is not positional syntax.
>
> The syntax is as follows :
>
> update lob (LOB ‘<lob handle>’, LOCATION < int64 address>, SIZE <
> int64 size>);
> This will take a lob handle as input (it could be an empty lob or have
> existing data). It will replace the contents with the data specified in
> LOCATION.
>
> update lob (LOB ‘<lob handle>’, LOCATION < int64 address>, SIZE <
> int64 size>, APPEND);
> This will take a lob handle as input (it could be an empty lob or have
> existing data). It will append the contents with the data specified in
> LOCATION.
>
> update lob (LOB ‘<lob handle>’, TRUNCATE);
> This will truncate the existing data and initialize the lob to empty_lob
> for the provided lob handle.
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