Getting Started with DB2 Express-C

Chapter 15 - DB2 pureXML 281
where $y/ResponseRequested=‘Yes’
return (
{$y/ProductID
$y/CustomerID
$y/Message}
)
Listing 15.19 - An example of the db2-fn:sqlquery function embedding SQL within
XQuery
In the example, the SQL query filters rows based on the condition that the srp column has
a value greater than 100. From those rows filtered, it will pick the comments column,
which is the XML column. Next XQuery (or XPath) is applied to go to sub-elements.
Note:
SQL is case insensitive and DB2 stores all table and column names in uppercase by
default. XQuery on the other hand, is case sensitive. The above functions are XQuery
interface functions so all the table names and column names should be passed to these
functions in uppercase. Passing the object names in lowercase may result in an undefined
object name error.
15.3.6 Joins with SQL/XML
This section describes how to perform JOIN operations between two XML columns of
different tables, or between one XML column and one relational column. Assume you have
created two tables with the statements shown in Listing 15.20
CREATE TABLE dept (unitID CHAR(8), deptdoc XML)
CREATE TABLE unit (unitID CHAR(8) primary key not null,
name CHAR(20),
manager VARCHAR(20),
...
)
Listing 15.20 - DDL of tables to use in the JOIN examples
You can perform a JOIN operation in either of two ways. The first method is shown in
Listing 15.21.
SELECT u.unitID
FROM dept d, unit u
WHERE XMLEXISTS (
‘$e//employee[name = $m]’
passing d.deptdoc as “e”, u.manager as “m”)
Listing 15.21 - First method to perform a JOIN with SQL/XML