Getting Started with DB2 Express-C

Chapter 15 - DB2 pureXML 283
15.3.8 Update and delete operations
Update and delete operations on XML data can be performed in one of two ways:
• Using SQL UPDATE and DELETE statements
• Using the TRANSFORM expression
For the first way using SQL UPDATE and DELETE statements, the update or delete occurs
at the document level; that is, the entire XML document is replaced with the updated one.
For example, in the UPDATE statement in Listing 15.25 below, if you’d only like to change
the element, the entire XML document is actually replaced.
UPDATE clients SET contact=(
xmlparse(document
‘
5401 Julio ave.
San Jose
CA
95116
4084633000
4081111111
4082222222
4087776666
newemail@someplace.com
')
)
WHERE id = 3227
Listing 15.25 - An example of an SQL UPDATE
For the second way, you can perform sub-document updates using the TRANSFORM
expression, which is a lot more efficient. This allows you to replace, insert, delete or
rename nodes in an XML document. You can also change the value of a node without
replacing the node itself, typically to change an element or attribute value–which is a very
common type of update. This support was added in DB2 9.5.
The TRANSFORM expression is part of the XQuery language, you can use it anywhere
you normally use XQuery, for example in a FLWOR expression or in the XMLQUERY
function in an SQL/XML statement. The most typical use is in an SQL UPDATE statement
to modify an XML document in an XML column.
Listing 15.26 shows the syntax of the TRANSFORM expression.
>>-transform--| copy clause |--| modify clause |--| return clause |-><
copy clause