database

The CRUD cycle describes the elemental functions of a persistent database. CRUD stands for Create, Read, Update and Delete. (Retrieve may occasionally be substituted for Read.) These functions are also descriptive of the data life cycle.

2. Clob vs Blob

LOB stands for large object, a stream of data stored in a database. Maximum capacity of a LOB is (4 gigabytes-1) bytes. In Oracle three kinds of LOB data type exist:

• BLOB datetype stores unstructured binary large objects. BLOB objects can be thought of as bitstreams with no character set semantics.

• The CLOB datatype stores single-byte and multibyte character data. Both fixed-width and variable-width character sets are supported, and both use the database character set.

• The NCLOB datatype stores Unicode data.

3. Truncate VS delete

Truncate: removes all data from a table, typically bypassing a number of integrity enforcing mechanisms.

delete: delete existing records in a table.

4. View vs Materalized View vs Table

Materalized view: disk based and are updated periodidcally based upon the query definition.

view: virtual only and run the query definition each time they are accessed.