The following bug has been logged online:

Bug reference: 1960
Logged by: tadayoshi sato
Email address: tsa1953 (AT) ace (DOT) ocn.ne.jp
PostgreSQL version: 8.0.4
Operating system: WindowsXp ,Linux (redhat9)
Description: Respons(Binary) is not correctly by PQexecParams
Details:

The result is made a binary with PQExecParams and it doesn't respond the
data of Varchar (The server: EUC-JP and client: SHIFTJIS) correctly.
The cause seems it is because the character string of the argument to
pg_server_to_client of the average of pq_sendtext is not NULL stop.

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