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[XML-DEV Mailing List Archive Home] [By Thread] [By Date] [Recent Entries] [Reply To This Message] [XQuery] FLWOR (for-let-where-order-return) equivalent to FOR (for-order
Hi Folks,
I am wondering about the value of the "let" and "where" clause in the XQuery
FLWOR expression. I believe that the same capability is possible simply by
using a for-order-return expression. If that is true, then I wonder about
the value of FLWOR (recent discussions seem to imply that FLWOR is one of
the "key advantages" of XQuery).
Let me give a couple of examples.
Example 1. Let's start with a simple example. Consider this XML document:
<?xml version="1.0"?>
<Numbers>
<Number>0</Number>
<Number>8</Number>
<Number>23</Number>
<Number>17</Number>
<Number>5</Number>
<Number>19</Number>
<Number>44</Number>
<Number>13</Number>
<Number>78</Number>
<Number>21</Number>
<Number>2</Number>
<Number>1</Number>
<Number>15</Number>
<Number>67</Number>
<Number>99</Number>
<Number>14</Number>
<Number>8</Number>
<Number>33</Number>
<Number>50</Number>
</Numbers>
Problem: output all the numbers less than 20, in ascending sorted order.
Here's how to do it using for-where-order-return:
for $i in //Number
where number($i) <= 20
order by number($i) ascending
return $i/text()
However, it could just as easily be accomplished with simply
for-order-return:
for $i in //Number[number(text()) <= 20]
order by number($i) ascending
return $i/text()
Thus, we see that for-order-return has the same capability as
for-where-order-return.
Example 2. Consider these two XML documents which contain information about
Fitness Center members:
<?xml version="1.0"?>
<MemberNames>
<Member id="1">
<Name>Jeff</Name>
</Member>
<Member id="2">
<Name>David</Name>
</Member>
.
</MemberNames>
<?xml version="1.0"?>
<MemberAges>
...
<Member id="1">
<Age>35</Age>
</Member>
<Member id="2">
<Age>39</Age>
</Member>
...
</MemberAges>
Problem: Join each Member's Name with their Age.
Here's how to do it using for-let-where-order-return:
for $i in //Member
let $j := doc("MemberAges.xml")//Member[@id eq $i/@id]/Age
where number($i/@id) <= 5
order by $i/Name/text() ascending
return
$i/Name/text(),
$j/text()
However, it could just as easily be accomplished with simply
for-order-return:
for $i in //Member[number(@id) <= 5], $j in
doc("MemberAges.xml")//Member[@id eq $i/@id]/Age
order by $i/Name/text() ascending
return
$i/Name/text(),
$j/text()
Thus, we see that for-order-return has the same capability as
for-let-where-order-return.
Is there something that can be done with for-let-where-order-return which
simply cannot be done with for-order-return? If not, then what value is
for-let-where-order-return? Is it simply "syntactic sugar"? /Roger
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