Oracle database from getting started to mastering four

Sequence
is a more important concept in Oracle
The transaction does not work for DDL
queries, updates, datasheets, constraints these concepts to master.

There is a data type in many databases-the autogrow column, which can
Create a serial number
12c did not provide such an auto-growing column before, if you want to use the auto-growing column
Can be done with a sequence.
The sequence belongs to the creation process of database objects, which belongs to the classification category of DDL.
For a sequence, it is saved in the data dictionary
SELECT * from User_sequences;
Time stamp + sequence

If you want to use a sequence, you can use the following two pseudo-columns
Nextval: Gets the next content value of the sequence. The value of each call sequence will grow.
Currval: Gets the current contents of the sequence, and each call does not grow.

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View
And the query is also related to the specific development requirements, then in the development process of the programmer to complete
is not all the contents of the database, but more should consider the design structure of the program, you can
Is that every project contains complex queries, so how can programmers be freed from complex queries?
So in this case, the concept of view is presented. The use of views enables encapsulation of complex SQL statements. From the actual open
In other words, a good database designer, in addition to giving a reasonable data table structure, should also be able to use all
The query is packaged as a view and presented to the developer.
A means of separating program tasks,
The Database Designer view (which is the interface of two types of people) is used by developers

Oracle database from getting started to mastering four