WL#1397: convert XML -> SQL

SUMMARY
-------

As a complement to --xml mode of mysqldump (and mysql) we can provide
an XSL that converts our XML dump to valid SQL dump. As far as I
understand it should be rather easy.


DECISIONS REGARDING THIS WL
---------------------------
- Jeffrey has decided that this is not for 5.1.
  Lars thinks this should be planned for 5.2.
  -- Lars, 2007-02-21

Please find the original information from the contributor here:

http://lists.mysql.com/internals/34169
http://lists.mysql.com/internals/34170


The final syntax is a little bit different:

LOAD XML [LOW_PRIORITY | CONCURRENT] [LOCAL] INFILE 'file_name'
    [REPLACE | IGNORE]
    INTO TABLE tbl_name
    [CHARACTER SET charset_name]
    [ROWS IDENTIFIED BY 'row_tag']
    [IGNORE number [LINES|ROWS]]
    [(col_name_or_user_var,...)]
    [SET col_name = expr,...)]

Difference comparing to the original Erik's patch:

1. "IGNORE 10 ROWS" is also understood as a synonym to "IGNORE 10 LINES",
because "lines" is something not well applicable to XML.
Note, as a side effect "IGNORE 10 ROWS" also works in "LOAD DATA" syntax.

2. "ROWS IDENTIFIER BY" is optional. The default tag is ''.

3. "CHARACTER SET charset_name" is also possible, like in "LOAD DATA".

LLD is found in the contributed patches for this feature.

There's a contributed patch from Erik Wetterberg
implementing "LOAD XML" syntax, hardcoded
to understand only the format of "mysqldump --xml" output,
but doing it very efficiently:

http://lists.mysql.com/commits/20059


There's also not-so-efficient XPath-based solution,
but it is not restricted to only "mysqldump --xml" format,
and can load data from any XML files, which can
be useful to import data from third party applications:

http://lists.mysql.com/commits/20060