Any command other than those documented in the ij command reference are handed to the current connection to execute directly. The statement's closing semicolon, used by ij to determine that it has ended, is not passed to the underlying connection. Only one statement at a time is passed to the connection. If the underlying connection itself accepts semicolon-separated statements (which Derby does not), they can be passed to the connection using ij's Execute command to pass in a command string containing semicolon-separated commands.
ij uses the result of the JDBC execute request to determine whether it should print a number-of-rows message or display a result set.
If a JDBC execute request causes an exception, it displays the SQLState, if any, and error message.
The number-of-rows message for inserts, updates, and deletes conforms to the JDBC specification for any SQL statement that does not have a result set. DDL (data definition language) commands typically report "0 rows inserted/updated/deleted" when they successfully complete.
To display a result set, ij formats a banner based on the JDBC ResultSetMetaData information returned from getColumnLabel and getColumnWidth. Long columns wrap the screen width, using multiple lines. An & character denotes truncation (ij limits displayed width of a column to 128 characters by default; see MaximumDisplayWidth).
ij displays rows as it fetches them. If the underlying DBMS materializes rows only as they are requested, ij displays a partial result followed by an error message if there is a error in fetching a row partway through the result set.
ij verifies that a connection exists before issuing statements against it and does not execute SQL when no connection has yet been made.
There is no support in ij for the JDBC feature multiple result sets.