Historical version. PostgreSQL 7.4 has reached end of support. See the current manual.
30.3. Closing a Connection
To close a connection, use the following statement:
EXEC SQL DISCONNECT [connection];The connection can be specified in the following ways:
connection-name
DEFAULT
CURRENT
ALL
If no connection name is specified, the current connection is closed.
It is good style that an application always explicitly disconnect from every connection it opened.
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Read the upstream documentation. For corrections, first check the current manual.