XQuery Built-in Functions

XQuery has a large library of built-in functions, which are all supported by DataDirect XQuery. The vast majority of these are translated into SQL. For some of these functions, the translation is straightforward; for others, the translation requires more thought. We do not know of another XQuery implementation in which such a high proportion of XQuery functions are executed directly in the database.

for $u in collection('USERS')/USERS
return concat($u/FIRSTNAME,$u/LASTNAME)

SELECT ALL
 {fn CONCAT(nrm5."FIRSTNAME",nrm5."LASTNAME")} AS RACOL1
FROM
 "PEPPINO"."USERS" nrm5

For most of the functions in the XQuery built-in library, though, translating to efficient SQL is non-trivial. DataDirect XQuery does this without changing the semantics of the XQuery function.

for $u in collection('USERS')/USERS
return substring-before($u/FIRSTNAME, 'lo')

SELECT ALL
  (CASE WHEN
     {fn LOCATE('lo',nrm5."FIRSTNAME")} > 0
   THEN
     {fn LEFT( nrm5."FIRSTNAME", {fn LOCATE('lo',nrm5."FIRSTNAME")} -1)}
   ELSE
     '' END) AS RACOL1
FROM
  "PEPPINO"."USERS" nrm5

This translation uses features found only in Oracle databases along with JDBC escapes that are standard, but not supported by all drivers - and these features are needed to implement substring-before() efficiently. Different features are used on other databases to achieve an efficient and conformant implementation.