|The PostgreSQL 9.0 Reference Manual - Volume 1A - SQL Language Reference
by The PostgreSQL Global Development Group
Paperback (6"x9"), 454 pages
RRP £14.95 ($19.95)
Sales of this book support the PostgreSQL project! Get a printed copy>>>
6.13.2 Encoding Handling
Care must be taken when dealing with multiple character encodings
on the client, server, and in the XML data passed through them.
When using the text mode to pass queries to the server and query
results to the client (which is the normal mode), PostgreSQL
converts all character data passed between the client and the
server and vice versa to the character encoding of the respective
end; see Volume 3: Character Set Support. This includes string
representations of XML values, such as in the above examples.
This would ordinarily mean that encoding declarations contained in
XML data can become invalid as the character data is converted
to other encodings while travelling between client and server,
because the embedded encoding declaration is not changed. To cope
with this behavior, encoding declarations contained in
character strings presented for input to the
are ignored, and content is assumed
to be in the current server encoding. Consequently, for correct
processing, character strings of XML data must be sent
from the client in the current client encoding. It is the
responsibility of the client to either convert documents to the
current client encoding before sending them to the server, or to
adjust the client encoding appropriately. On output, values of
xml will not have an encoding declaration, and
clients should assume all data is in the current client
When using binary mode to pass query parameters to the server and query results back to the client, no character set conversion is performed, so the situation is different. In this case, an encoding declaration in the XML data will be observed, and if it is absent, the data will be assumed to be in UTF-8 (as required by the XML standard; note that PostgreSQL does not support UTF-16). On output, data will have an encoding declaration specifying the client encoding, unless the client encoding is UTF-8, in which case it will be omitted.
Needless to say, processing XML data with PostgreSQL will be less error-prone and more efficient if the XML data encoding, client encoding, and server encoding are the same. Since XML data is internally processed in UTF-8, computations will be most efficient if the server encoding is also UTF-8.
Caution: Some XML-related functions may not work at all on non-ASCII data when the server encoding is not UTF-8. This is known to be an issue for
|ISBN 9781906966041||The PostgreSQL 9.0 Reference Manual - Volume 1A - SQL Language Reference||See the print edition|