XQuery Sequence Functions

XQuery is a query and functional programming language that allows you to work with XML and other structured data formats. One of the essential features of XQuery is the ability to work with sequences of items.

A sequence is an ordered collection of values, and it can contain any number of items, including nodes, atomic values, and other sequences. XQuery provides a large number of built-in functions for working with sequences, and in this article, we’ll introduce some of the most useful ones.

Sequence Constructors

To create a sequence of values, you can use the sequence constructor function (_) or the comma operator (,). For example:

let $seq := (1, 2, 3)
return $seq

In this example, the sequence constructor is used to create a sequence of three integer values (1, 2, and 3), which are stored in the $seq variable.

Sequence Functions

count()

The count() function returns the number of items in a sequence:

let $seq := (1, 2, 3)
return count($seq)

Output:

3

empty()

The empty() function returns true if a sequence is empty:

let $empty_seq := ()
return empty($empty_seq)

Output:

true

exists()

The exists() function returns true if a sequence contains at least one item:

let $seq := (1, 2, 3)
return exists($seq)

Output:

true

concat()

The concat() function concatenates two or more sequences into a single sequence:

let $seq1 := (1, 2, 3)
let $seq2 := (4, 5, 6)
return concat($seq1, $seq2)

Output:

1 2 3 4 5 6

distinct-values()

The distinct-values() function returns a sequence containing the distinct values in a given sequence:

let $seq := (1, 2, 3, 1, 2, 3)
return distinct-values($seq)

Output:

1 2 3

first()

The first() function returns the first item in a sequence:

let $seq := (1, 2, 3)
return first($seq)

Output:

1

last()

The last() function returns the last item in a sequence:

let $seq := (1, 2, 3)
return last($seq)

Output:

3

reverse()

The reverse() function returns a sequence containing the items of a given sequence in reverse order:

let $seq := (1, 2, 3)
return reverse($seq)

Output:

3 2 1

subsequence()

The subsequence() function returns a subsequence of a given sequence:

let $seq := (1, 2, 3, 4, 5)
return subsequence($seq, 2, 3)

Output:

2 3 4

min()

The min() function returns the minimum value in a sequence:

let $seq := (5, 3, 10, 1)
return min($seq)

Output:

1

max()

The max() function returns the maximum value in a sequence:

let $seq := (5, 3, 10, 1)
return max($seq)

Output:

10

sum()

The sum() function returns the sum of the values in a sequence:

let $seq := (1, 2, 3)
return sum($seq)

Output:

6

avg()

The avg() function returns the average value of the values in a sequence:

let $seq := (1, 2, 3)
return avg($seq)

Output:

2

Conclusion

In this article, we have introduced several useful XQuery sequence functions for working with sequences of items, including count(), empty(), concat(), distinct-values(), first(), last(), reverse(), subsequence(), min(), max(), sum(), and avg(). These functions can help you manipulate and transform your data effectively when querying XML and other structured data formats with XQuery.