Managing Databases with Oracle
Which of the following is not true about modifying table columns?

You can drop a column at any time.
You can increase the number of characters in character columns or the number of digits in numeric columns
You can add a column at any time as long as it is a NULL column.
You cannot increase or decrease the number of decimal places.

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Managing Databases with Oracle
An Oracle System Change Number (SCN):

is a value that keeps track of explicit locks.
is a value that is incremented whenever a dirty read occurs.
is a value that is incremented whenever database changes are made.
is incremented whenever a deadlock occurs.

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