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Conditional expressions

XQuery supports a general if-then-else construction.

The example query: 
for $h in document("library.xml")//holding
return
  <holding>
    { $h/title,
      if ($h/@type = "Journal")
      then $h/editor
      else $h/author
    }
  </holding>

extracts from the holdings of a library the titles and either editors or authors.

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