An optional charset that will be used temporarily while sending
query to the server. If necessary, a query
SET character_set_client=charset
is sent to the server first, then query is sent as-is, and then
the connection charset is restored again (if necessary).
Primarily useful with charset set to "latin1"
if
unicode encode mode (see set_unicode_encode_mode ) is enabled
(the default) and you have some large queries (typically blob
inserts) where you want to avoid the query parsing overhead.