DISCONNECT — terminate a database connection
DISCONNECT connection_name
DISCONNECT [ CURRENT ]
DISCONNECT ALL
     DISCONNECT closes a connection (or all
     connections) to the database.
    
connection_name
        A database connection name established by
        the CONNECT command.
       
CURRENT
        Close the “current” connection, which is either
        the most recently opened connection, or the connection set by
        the SET CONNECTION command.  This is also
        the default if no argument is given to
        the DISCONNECT command.
       
ALLClose all open connections.
int
main(void)
{
    EXEC SQL CONNECT TO testdb AS con1 USER testuser;
    EXEC SQL CONNECT TO testdb AS con2 USER testuser;
    EXEC SQL CONNECT TO testdb AS con3 USER testuser;
    EXEC SQL DISCONNECT CURRENT;  /* close con3          */
    EXEC SQL DISCONNECT ALL;      /* close con2 and con1 */
    return 0;
}
     DISCONNECT is specified in the SQL standard.