XQuery [value()]: 'value()' requires a singleton (or empty sequence), found operand of type 'xdt:untypedAtomic *'

Question

I\'m trying to insert rows into a table using a select from XML. I think I\'m close. Where am I going wrong?

declare @xmldata xml;
set @xmldata = \'

        

Answer 1

Struggling with a similar problem, and found that @birdus's answer didn't work if you have additional layers of nesting in your xml that you were referencing in your XQuery, e.g. supposing a slightly different XML shape, if you had

T.x.value('PurchasePlace/PurchaseCity[1]','varchar(50)')

you would still get the singleton error. Though @birdus's solution does work for this specific case a more generally applicable solution that combines the best of @birdus's & @Mikael-Eriksson's solution is to do:

insert into PurchaseDetails(Upc, Quantity, PurchaseDate, PurchaseCity, PurchaseState)
select T.X.value('(Upc)[1]', 'char(11)'),
T.X.value('(Quantity)[1]', 'int'),
T.X.value('(PurchaseDate)[1]', 'varchar(7)'),
T.X.value('(PurchaseCity)[1]', 'varchar(50)'),
T.X.value('(PurchaseState)[1]', 'char(2)')
from @xmlData.nodes('/Database/PurchaseDetails/PurchaseDetail') as T(X)

This combine's @birdus's omission of /text(), which is superfluous, but adds @Mikael-Eriksson's parentheses around the element selector, to allow multiple element selectors as in my modified example which becomes:

T.x.value('(PurchasePlace/PurchaseCity)[1]','varchar(50)')

The reason for this, that a few have asked about, is not that @birdus's version returns something other than a singleton in any of the examples discussed here, but that it might. Per Microsoft Docs:

Location steps, function parameters, and operators that require singletons will return an error if the compiler cannot determine whether a singleton is guaranteed at run time.