How to extract text content from an XML document at a given location using the EXTRACTVALUE() function?

EXTRACTVALUE(xml, path) is a MySQL built-in function that extracts text content from an XML document at a given location. For example:

SET @xml = 'XY';

SELECT EXTRACTVALUE(@xml, '//b[1]'), EXTRACTVALUE(@xml, '//b[2]');
  -- +------------------------------+------------------------------+
  -- | EXTRACTVALUE(@xml, '//b[1]') | EXTRACTVALUE(@xml, '//b[2]') |
  -- +------------------------------+------------------------------+
  -- | X                            | Y                            |
  -- +------------------------------+------------------------------+

SELECT EXTRACTVALUE(@xml, '/a'), EXTRACTVALUE(@xml, '//b');
  -- +--------------------------+---------------------------+
  -- | EXTRACTVALUE(@xml, '/a') | EXTRACTVALUE(@xml, '//b') |
  -- +--------------------------+---------------------------+
  -- |                          | X Y                       |
  -- +--------------------------+---------------------------+

SELECT EXTRACTVALUE(@xml, 'count(//b)'), EXTRACTVALUE(@xml, 'count(//c)');
  -- +----------------------------------+----------------------------------+
  -- | EXTRACTVALUE(@xml, 'count(//b)') | EXTRACTVALUE(@xml, 'count(//c)') |
  -- +----------------------------------+----------------------------------+
  -- | 2                                | 0                                |
  -- +----------------------------------+----------------------------------+

Note that variables used in the location path must be escaped with the '$' prefix. For example,

SET @i =1, @j = 2;

SELECT EXTRACTVALUE(@xml, '//b[$@i]'), EXTRACTVALUE(@xml, '//b[$@j]');
  -- +--------------------------------+--------------------------------+
  -- | EXTRACTVALUE(@xml, '//b[$@i]') | EXTRACTVALUE(@xml, '//b[$@j]') |
  -- +--------------------------------+--------------------------------+
  -- | X                              | Y                              |
  -- +--------------------------------+--------------------------------+

Reference information of the EXTRACTVALUE() function:

EXTRACTVALUE(xml, path): str
  Extracts text content from an XML document at a given location.

Arguments, return value and availability:
  xml: Required. The XML document to be extracted from.
  path: Required. The location path where the value to be extracted.
  str: Return value. The extracted text content.
  Available since MySQL 4.0.

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