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<H1><A name="RDBDASC%2B%2BPartialUpdate-PartialUpdate"></A>PartialUpdate</H1>
<P>The RDB DAS uses the SDO Change Summary to generate a set of database write operations. Rather than generated a statement to update all columns in a table that maps to a SDO DataObject Type, the DAS generates statements that update ony those columns that map to a modified DataObject property. For example, consider a Customer DataObject that has had the LastName property changed. The <B>partial update</B> statement generated by the DAS will look something like this:</P>
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<PRE>UPDATE CUSTOMER SET LASTNAME = 'Tuscany' WHERE ID = '1'
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<P>Rather than a statement that updates all columns like this:</P>
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<PRE>UPDATE CUSTOMER SET FIRSTNAME = 'APACHE', SET LASTNAME = 'TUSCANY', SET ADDRESS = 'USA', SET PHONE = '555-5555', SET AGE = '7', SET SHOESIZE = '15' WHERE ID = '1'
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<P>There are a couple of very good reasons for using a partial update approach. For one, a performance boost can be realized by applications writing to wide tables. For example, tables with over 100 columns are not unheard of. It can be a huge waste of resource to update 100 columns when only one was modified. Another reason for partial update is that some databases employ <SPAN class="nobr"><A href="http://en.wikipedia.org/wiki/Database_trigger" title="Visit page outside Confluence" rel="nofollow">triggers<SUP><IMG class="rendericon" src="http://cwiki.apache.org/confluence/images/icons/linkext7.gif" height="7" width="7" align="absmiddle" alt="" border="0"></SUP></A></SPAN>on specific columns in a table. Partial updates are necessary when column triggers are employed to avoid tripping the trigger on every row update rather than only on updates to the specific column. </P>
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