SQL Module

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

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

Signature	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

Updated with Version 11: Optional credentials.

Signature	sql:connect( $url as xs:string, $options as map(*)? := 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>]. Values specified for $username and $password are used as credentials for connecting to the database. The $options parameter can be used to set connection options.
Errors	error: an SQL exception occurred when connecting to the database.
Examples	Connects to an SQL Server and sets autocommit to true: sql:connect('dbc:sqlserver://DBServer', map { 'autocommit': true() })

sql:execute

Signature	sql:execute( $id as xs:anyURI, $statement as xs:string, $options as map(*)? := 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 error occurred while executing SQL. id: the specified connection does not exist. timeout: query execution exceeded timeout.

sql:execute-prepared

Signature	sql:execute-prepared( $id as xs:anyURI, $params as element(sql:parameters), $options as map(*)? := 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 { "bigdecimal" | "boolean" | "byte" | "date" | "double" | "float" | "int" | "long" | "short" | "sqlxml" | "string" | "time" | "timestamp" }, 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 error occurred while executing SQL. id: the specified connection does not exist. parameters: no parameter type specified. timeout: query execution exceeded timeout. type: the value of a parameter cannot be converted to the specified format.

sql:prepare

Signature	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 error occurred while executing SQL. id: the specified connection does not exist.

sql:commit

Signature	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 error occurred while executing SQL. id: the specified connection does not exist.

sql:rollback

Signature	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 error occurred while executing SQL. id: the specified connection does not exist.

sql:close

Signature	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 error occurred while executing SQL. 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">3.5</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 with 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

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	No parameter type specified.
timeout	Query execution exceeded timeout.
type	The value of a parameter cannot be converted to the specified format.

Changelog

Version 11

• Updated: sql:connect: Optional credentials.

Version 9.6

• Updated: sql:execute-prepared, additional types added

Version 9.0

• Updated: sql:execute, sql:execute-prepared: Return update count for updating statements. $options argument added.
• Updated: Connection ids are URIs now.
• Updated: error codes updated; errors now use the module namespace

Version 7.5

• Updated: prepared statements are now executed via sql:execute-prepared

The module was introduced with Version 7.0.