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1.7. Functions Associated with the COPY Command

The COPY command in PostgreSQL has options to read from or write to the network connection used by libpq. Therefore, functions are necessary to access this network connection directly so applications may take advantage of this capability.

These functions should be executed only after obtaining a PGRES_COPY_OUT or PGRES_COPY_IN result object from PQexec or PQgetResult.

When using PQgetResult, the application should respond to a PGRES_COPY_OUT result by executing PQgetline repeatedly, followed by PQendcopy after the terminator line is seen. It should then return to the PQgetResult loop until PQgetResult returns NULL. Similarly a PGRES_COPY_IN result is processed by a series of PQputline calls followed by PQendcopy, then return to the PQgetResult loop. This arrangement will ensure that a copy in or copy out command embedded in a series of SQL commands will be executed correctly.

Older applications are likely to submit a copy in or copy out via PQexec and assume that the transaction is done after PQendcopy. This will work correctly only if the copy in/out is the only SQL command in the command string.