From the screenshot it seems you are using SQL Developer, which has a slightly complicated way of displaying dbms_output. First you have to show the dbms_output pane using View > DBMS_OUTPUT. Then you have to enable it by pressing the green "+" symbol in the dbms_output pane.
From the Tools menu (or on OS X, the SQL Developer menu) go to Preferences. In versions up to 4.1.5, in the preference pane expand the Database section, and then the SQL Formatter section. The top level lets you import and export settings, and the Oracle Formatting section lets you choose how you want your code to be formatted. You can have multiple profiles with their own specific formatting ...
An update SQL query was executed on the server, which caused many problems later. How can I get the list of update queries executed in last 2 months, so that I can trace the exact problematic SQL ...
1 When using SQuirreL SQL, it is common to configure the connection details, including the service name, in the "tnsnames.ora" file. By placing the "tnsnames.ora" file within the project directory, it allows SQuirreL SQL to locate and use the connection details defined in that file for establishing database connections.
Overall I would like to have a dark theme for Oracle SQL Developer. I know that I can go to the menu item Window/Preferences, Code Editor/PL/SQL Syntax Colors and select the "Twilight" Scheme and the SQL Worksheet window will look as expected.
In Oracle SQL Developer, if I'm viewing the information on a table, I can view the constraints, which let me see the foreign keys (and thus which tables are referenced by this table), and I can view the dependencies to see what packages and such reference the table.
Another version from May 2011: Getting Started with Oracle SQL Developer For more info check this related question: How to create a new database after initally installing oracle database 11g Express Edition?
I don't see any tables in the tables section of a database that I've linked to w/ SQL developer. The DB admin says I need to change the default schema in SQL developer. How do I do that?
Oracle SQL Developer Soars mentions, that if you have Oracle client software and a tnsnames.ora file already installed on your machine, Oracle SQL Developer will automatically populate the Connections navigator from the net service names defined in tnsnames.ora.
