XQuery FLWOR

FLWOR is the heart of XQuery. It stands for For, Let, Where, Order by, Return — five clauses that combine to form a complete query expression. FLWOR is to XQuery what SELECT-FROM-WHERE-ORDER BY is to SQL. Once you understand FLWOR, you can write complex XQuery queries that filter, sort, group, and reshape XML data.

FLWOR Structure

for $variable in expression     ← iterate over a sequence
let $variable := expression     ← bind a value to a variable
where condition                 ← filter results
order by expression             ← sort results
return expression               ← define the output for each iteration

Only for and return are required. The others are optional.

Working XML File: employees.xml

<company>
  <employee dept="Engineering">
    <name>Arjun Kumar</name><salary>85000</salary><experience>5</experience>
  </employee>
  <employee dept="Design">
    <name>Meena Pillai</name><salary>72000</salary><experience>3</experience>
  </employee>
  <employee dept="Engineering">
    <name>Ravi Sharma</name><salary>91000</salary><experience>8</experience>
  </employee>
  <employee dept="HR">
    <name>Sunita Joshi</name><salary>58000</salary><experience>2</experience>
  </employee>
</company>

The for Clause

The for clause binds each node in a sequence to a variable, one at a time. The dollar sign $ marks a variable in XQuery.

for $emp in doc("employees.xml")/company/employee
return $emp/name

Output

<name>Arjun Kumar</name>
<name>Meena Pillai</name>
<name>Ravi Sharma</name>
<name>Sunita Joshi</name>

The where Clause — Filtering

The where clause filters iterations — only those where the condition is true produce output.

for $emp in doc("employees.xml")/company/employee
where $emp/salary > 75000
return $emp/name

Output — only high earners

<name>Arjun Kumar</name>
<name>Ravi Sharma</name>

The order by Clause — Sorting

The order by clause sorts results before returning them. Add descending for reverse order; default is ascending.

for $emp in doc("employees.xml")/company/employee
order by $emp/salary descending
return
  <result>
    <name>{ $emp/name/text() }</name>
    <salary>{ $emp/salary/text() }</salary>
  </result>

Output — sorted highest salary first

<result><name>Ravi Sharma</name><salary>91000</salary></result>
<result><name>Arjun Kumar</name><salary>85000</salary></result>
<result><name>Meena Pillai</name><salary>72000</salary></result>
<result><name>Sunita Joshi</name><salary>58000</salary></result>

The let Clause — Variables

The let clause assigns a value or sequence to a variable for use later in the query. Unlike for, let does not create a loop — it binds the whole sequence at once.

let $allEmployees := doc("employees.xml")/company/employee
let $avgSalary := avg($allEmployees/salary)
return
  <summary>
    <totalEmployees>{ count($allEmployees) }</totalEmployees>
    <averageSalary>{ $avgSalary }</averageSalary>
  </summary>

Output

<summary>
  <totalEmployees>4</totalEmployees>
  <averageSalary>76500</averageSalary>
</summary>

Complete FLWOR with All Clauses

A query that finds Engineering employees, calculates a bonus, and returns sorted results:

let $bonus-rate := 0.15
for $emp in doc("employees.xml")/company/employee
where $emp/@dept = "Engineering"
order by $emp/salary descending
return
  <engineerReport>
    <name>{ $emp/name/text() }</name>
    <salary>{ $emp/salary/text() }</salary>
    <bonus>{ $emp/salary * $bonus-rate }</bonus>
    <years>{ $emp/experience/text() }</years>
  </engineerReport>

Output

<engineerReport>
  <name>Ravi Sharma</name>
  <salary>91000</salary>
  <bonus>13650</bonus>
  <years>8</years>
</engineerReport>
<engineerReport>
  <name>Arjun Kumar</name>
  <salary>85000</salary>
  <bonus>12750</bonus>
  <years>5</years>
</engineerReport>

FLWOR vs SQL Comparison

Nested FLWOR Expressions

FLWOR expressions can nest inside each other to handle hierarchical data.

for $dept in distinct-values(doc("employees.xml")/company/employee/@dept)
return
  <department name="{ $dept }">
  {
    for $emp in doc("employees.xml")/company/employee[@dept = $dept]
    order by $emp/name
    return <member>{ $emp/name/text() }</member>
  }
  </department>

Output

<department name="Design">
  <member>Meena Pillai</member>
</department>
<department name="Engineering">
  <member>Arjun Kumar</member>
  <member>Ravi Sharma</member>
</department>
<department name="HR">
  <member>Sunita Joshi</member>
</department>

Key Points to Remember

• FLWOR stands for For, Let, Where, Order by, Return.
• for and return are the only required clauses.
• for iterates over a sequence; let binds a whole sequence to a variable at once.
• where filters — only matching iterations produce output.
• order by sorts the results; add descending for reverse order.
• return defines the output structure — it can contain XML literals with {} expressions.
• FLWOR expressions can nest to handle multi-level XML hierarchies.