XQuery Module

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This XQuery Module contains functions for evaluating XQuery strings and modules at runtime.

Conventions

Template:Mark:

All functions and errors in this module are assigned to the http://basex.org/modules/xquery namespace, which is statically bound to the xquery prefix.

Functions

This XQuery Module contains functions to access relational databases from XQuery using SQL. With this module, you can execute query, update and prepared statements, and the result sets are returned as sequences of XML elements representing tuples. Each element has children representing the columns returned by the SQL statement.

This module uses JDBC to connect to a SQL server. Hence, your JDBC driver will need to be added to the classpath, too. If you work with the full distributions of BaseX, you can copy the driver into the lib directory. To connect to MySQL, for example, download the Connector/J Driver and extract the archive into this directory.

Conventions

Template:Mark:

All functions and errors in this module are assigned to the http://basex.org/modules/sql namespace, which is statically bound to the sql prefix.

Functions

sql:init

Signatures sql:init($class as xs:string) as empty-sequence()
Summary This function initializes a JDBC driver specified via $class. This step might be superfluous if the SQL database is not embedded.
Errors init: the specified driver is not found.

sql:connect

Signatures sql:connect($url as xs:string) as xs:anyURI
sql:connect($url as xs:string, $user as xs:string, $password as xs:string) as xs:anyURI
sql:connect($url as xs:string, $user as xs:string, $password as xs:string, $options as map(*)) as xs:anyURI
Summary This function establishes a connection to a relational database and returns a connection id. The parameter $url is the URL of the database and shall be of the form: jdbc:<driver name>:<server> [/<database>]. If the parameters $user and $password are specified, they are used as credentials for connecting to the database. The $options parameter can be used to set connection options.
Errors error: an SQL exception occurs, e.g. missing JDBC driver or not existing relation.
Examples Connects to an SQL Server and sets autocommit to true:
sql:connect('dbc:sqlserver://DBServer', map { 'autocommit': true() })

sql:execute

Template:Mark: Return update count for updating statements. $options argument added.

Signatures sql:execute($id as xs:anyURI, $statement as xs:string) as item()*
sql:execute($id as xs:anyURI, $statement as xs:string, $options as map(*)) as item()*
Summary This function executes an SQL $statement, using the connection with the specified $id. The returned result depends on the kind of statement:
  • If an update statement was executed, the number of updated rows will be returned as integer.
  • Otherwise, an XML representation of all results will be returned.

With $options, the following parameter can be set:

  • timeout: query execution will be interrupted after the specified number of seconds.
Errors error: an SQL exception occurs, e.g. not existing relation is retrieved.
id: the specified connection does not exist.

sql:execute-prepared

Template:Mark: Return update count for updating statements.

Signatures sql:execute-prepared($id as xs:anyURI, $params as element(sql:parameters)) as item()*
sql:execute-prepared($id as xs:anyURI, $params as element(sql:parameters), $options as map(*)) as item()*
Summary This function executes a prepared statement with the specified $id. The output format is identical to sql:execute. The optional parameter $params is an element <sql:parameters/> representing the parameters for a prepared statement along with their types and values. The following schema shall be used:
element sql:parameters {
  element sql:parameter {
    attribute type { "int" | "string" | "boolean" | "date" | "double" |
      "float" | "short" | "time" | "timestamp" | "sqlxml" },
    attribute null { "true" | "false" }?,
    text
  }+
}?

With $options, the following parameter can be set:

  • timeout: query execution will be interrupted after the specified number of seconds.
Errors attribute: an attribute different from type and null is set for a <sql:parameter/> element.
error: an SQL exception occurs, e.g. not existing relation is retrieved.
id: the specified connection does not exist.
parameters: wrong number of <sql:parameter/> elements, or parameter type is not specified.
type: the value of a parameter cannot be converted to the specified format.

sql:prepare

Signatures sql:prepare($id as xs:anyURI, $statement as xs:string) as xs:anyURI
Summary This function prepares an SQL $statement, using the specified connection $id, and returns the id reference to this statement. The statement is a string with one or more '?' placeholders. If the value of a field has to be set to NULL, then the attribute null of the <sql:parameter/> element must be true.
Errors error: an SQL exception occurs.
id: the specified connection does not exist.

sql:commit

Signatures sql:commit($id as xs:anyURI) as empty-sequence()
Summary This function commits the changes made to a relational database, using the specified connection $id.
Errors error: an SQL exception occurs.
id: the specified connection does not exist.

sql:rollback

Signatures sql:rollback($id as xs:anyURI) as empty-sequence()
Summary This function rolls back the changes made to a relational database, using the specified connection $id.
Errors error: an SQL exception occurs.
id: the specified connection does not exist.

sql:close

Signatures sql:close($id as xs:anyURI) as empty-sequence()
Summary This function closes a database connection with the specified $id.
Opened connections will automatically be closed after the XQuery expression has been evaluated, but in order to save memory, it is always recommendable to close connections that are not used anymore.
Errors error: an SQL exception occurs.
id: the specified connection does not exist.

Examples

Direct queries

A simple select statement can be executed as follows:

let $id := sql:connect("jdbc:postgresql://localhost:5432/coffeehouse")
return sql:execute($id, "SELECT * FROM coffees WHERE price < 10")

The result may look like:

<sql:row xmlns:sql="http://basex.org/modules/sql">
  <sql:column name="cof_name">French_Roast</sql:column>
  <sql:column name="sup_id">49</sql:column>
  <sql:column name="price">9.5</sql:column>
  <sql:column name="sales">15</sql:column>
  <sql:column name="total">30</sql:column>
</sql:row>
<sql:row xmlns:sql="http://basex.org/modules/sql">
  <sql:column name="cof_name">French_Roast_Decaf</sql:column>
  <sql:column name="sup_id">49</sql:column>
  <sql:column name="price">7.5</sql:column>
  <sql:column name="sales">10</sql:column>
  <sql:column name="total">14</sql:column>
</sql:row>

Prepared Statements

A prepared select statement can be executed in the following way:

(: Establish a connection :)
let $conn := sql:connect("jdbc:postgresql://localhost:5432/coffeehouse")
(: Obtain a handle to a prepared statement :)
let $prep := sql:prepare($conn, "SELECT * FROM coffees WHERE price < ? AND cof_name = ?")
(: Values and types of prepared statement parameters :)
let $params := <sql:parameters>
                 <sql:parameter type='double'>10</sql:parameter>
                 <sql:parameter type='string'>French_Roast</sql:parameter>
               </sql:parameters>
(: Execute prepared statement :)
return sql:execute-prepared($prep, $params)

SQLite

The following expression demonstrates how SQLite can be addressed using the Xerial SQLite JDBC driver:

(: Initialize driver :)
sql:init("org.sqlite.JDBC"),
(: Establish a connection :)
let $conn := sql:connect("jdbc:sqlite:database.db")
return (
  (: Create a new table :)
  sql:execute($conn, "drop table if exists person"),
  sql:execute($conn, "create table person (id integer, name string)"),
  (: Run 10 updates :)
  for $i in 1 to 10
  let $q := "insert into person values(" || $i || ", '" || $i || "')"
  return sql:execute($conn, $q),
  (: Return table contents :)
  sql:execute($conn, "select * from person")
)

Errors

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Code Description
attribute An attribute different from type and null is set for a <sql:parameter/> element.
error An SQL exception occurred.
id A connection does not exist.
init A database driver is not found.
parameters Wrong number of <sql:parameter/> elements, or parameter type is not specified.
type The value of a parameter cannot be converted to the specified format.

Changelog

Version 9.0
  • Updated: Connection ids are URIs now.
  • Updated: error codes updated; errors now use the module namespace
Version 7.5

The module was introduced with Version 7.0.

xquery:eval-update

Template:Mark: Renamed (old name: xquery:update)

Signatures xquery:eval-update($query as xs:string) as item()*
xquery:eval-update($query as xs:string, $bindings as map(*)?) as item()*
xquery:eval-update($query as xs:string, $bindings as map(*)?, $options as map(xs:string, xs:string)) as item()
Summary Evaluates $query as updating XQuery expression at runtime.
All updates will be added to the Pending Update List of the main query and performed after the evaluation of the main query.
The rules of the $bindings and $options parameters are the same as for xquery:eval.
Errors update: the query contains no updating expressions.
permission: insufficient permissions for evaluating the query.
timeout: query execution exceeded timeout.
limit: query execution exceeded memory limit.
nested: nested query evaluation is not allowed.
Any other error that may occur while evaluating the query.

xquery:invoke

Signatures xquery:invoke($uri as xs:string) as item()*
xquery:invoke($uri as xs:string, $bindings as map(*)?) as item()*
xquery:invoke($uri as xs:string, $bindings as map(*)?, $options as map(*)) as item()*
Summary Evaluates the XQuery module located at $uri at runtime and returns the resulting items. A relative URI will be resolved against the static base URI of the query.
The rules of the $bindings and $options parameters are the same as for xquery:eval.
Errors update: the expression contains updating expressions.
permission: insufficient permissions for evaluating the query.
BXXQ0004: query execution exceeded timeout.
nested: nested query evaluation is not allowed.
Any other error that may occur while evaluating the query.

xquery:invoke-update

Signatures xquery:invoke-update($uri as xs:string) as item()*
xquery:invoke-update($uri as xs:string, $bindings as map(*)?) as item()*
xquery:invoke-update($uri as xs:string, $bindings as map(*)?, $options as map(*)) as item()*
Summary Evaluates the updating XQuery module located at $uri at runtime. A relative URI will be resolved against the static base URI of the query.
The rules of the $bindings and $options parameters are the same as for xquery:eval.
Errors update: the expression contains no updating expressions.
permission: insufficient permissions for evaluating the query.
BXXQ0004: query execution exceeded timeout.
nested: nested query evaluation is not allowed.
Any other error that may occur while evaluating the query.

xquery:parse

Template:Mark: base-uri option added.

Signatures xquery:parse($query as xs:string) as item()?
xquery:parse($query as xs:string, $options as map(*)) as item()?
Summary Parses the specified $query string as XQuery module and returns the resulting query plan. The $options parameter influences the output:
  • compile: additionally compiles the query after parsing it. By default, this option is false.
  • plan: returns an XML representation of the internal query plan. By default, this option is true. The naming of the expressions in the query plan may change over time
  • pass: passes on the original error info (line and column number, optional file uri). By default, this option is false.
  • base-uri: set base-uri property for the query. This URI will be used when resolving relative URIs by functions such as fn:doc.
Errors Any error that may occur while parsing the query.
Examples
  • xquery:parse("1 + 3") returns:
<MainModule updating="false">
  <QueryPlan compiled="false">
    <Arith op="+">
      <Int value="1" type="xs:integer"/>
      <Int value="3" type="xs:integer"/>
    </Arith>
  </QueryPlan>
</MainModule>

xquery:parse-uri

Template:Mark: base-uri option added.

Signatures xquery:parse-uri($uri as xs:string) as item()?
xquery:parse-uri($uri as xs:string, $options as map(*)) as item()?
Summary Parses the XQuery module located at $uri and returns the resulting query plan. A relative URI will be resolved against the static base URI of the query. The rules for the $options parameter are the same as for xquery:parse.
Errors Any error that may occur while parsing the query.

Parallelized Execution

Parallel query execution is recommendable if you have various calls that require a lot of time, but cannot be sped up by rewriting the code. This is e. g. the case if external URLs are called. If you are parallelizing local data reads (such as the access to a database), single-threaded queries will usually be faster, because parallelized access to disk data often results in randomized access patterns, which can hardly be optimized by the caching strategies of HD, SSD or operating system.

xquery:fork-join

Signatures xquery:fork-join($functions as function(*)*) as item()*
Summary This function executes the supplied (non-updating) functions in parallel.
Examples
  • The following function sleeps in parallel; it will be finished in 1 second if your system has at least 2 cores:
let $f := function() { prof:sleep(1000) }
return xquery:fork-join(($f, $f))
  • In the following query, up to four URLs will be requested in parallel:
let $funcs :=
  for $segment in 1 to 4
  let $url := 'http://url.com/path' || $segment
  return function() { http:send-request((), $url) }
return xquery:fork-join($funcs)
Errors error: an unexpected error occurred.

Errors

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Code Description
permission Insufficient permissions for evaluating the query.
update updating expression found or expected.
timeout Query execution exceeded timeout.
memory Query execution exceeded memory limit.
nested Nested query evaluation is not allowed.
error An unexpected error occurred.

Changelog

Version 9.0
Version 8.5
Version 8.4
Version 8.0
Version 7.8.2
  • Added: $options argument
Version 7.8
  • Added: xquery:evaluate
  • Updated: used variables must be explicitly declared in the query string.

This module was introduced with Version 7.3. Functions have been adopted from the obsolete Utility Module.