SQL general     Last updated on 2009     10     3, a full moon day

1st to understand OSI layers existence in an era of binary to duo-binary ... 。

            Difficulties are:

            so many N protocols exist in Network_layer。

            so many N sessions [assuming 1 window is 1 session] exist in Session_layer。

            so many N RDBMS systems such as:

DB2。,

Microsoft Access。,

MySQL。,

Oracle。,

PostgreSQL。,

SQL Server。,

... 。

            so many N languages can program all layers in OSI such as C#, Java, Perl, Ruby, ... 。

            so many N frames exist Physical_layer。

            ...

2nd to understand ER model and its relational concept。

            Difficulties are:

            so many N meta data relationships exist in Logic_link_layer。

            so many N nested and complex mapping exists, therefore must understand "complex", and "mapping" and then nested statements, for example SELECT columnABC from tableXYZ WHERE SELECT  very simple 2 nested "selects" statement is here, and notice that WHERE statement makes 1 nested condition such as IJK and LMN tables join together with all columns inside, and also notice that the very simple 2 nested "selects" statement does not contain databases' storage allocation and file system formats either  * from tableIJK and tableLMN is a simple statement, however when involving transactions in several databases combination with Network_layer protocols AND programming language AND SQL syntax AND SQL semantic becomes security concern。

            ...

3rd to understand relational algebra and relational calculus。

            Difficulties are:

            so many N containers exist in Transport_layer。

            so many N embedded applications exist in Application_layer and Presentation_layer。

            ...

4th to understand SQL syntax and SQL semantic。

            Difficulties are:

            so many N tables exist in a database。

            so many N columns exist in a table。

            so many N file formats in a system。

            so many . dots in a system, i.e. abcCONTAINER.efgDATABASE.ijkTABLE.xyzCOLUMN

            ...

5th to understand data processing。

            Difficulties are:

            so many N human beings' error is the most difficult to query, to trace, ... 。

            so many N levels of human beings, such as ... , 2 zeros, 3 zeros, 4 zeros, 5 zeros, ... diff accountings ... 。

            One & only 1 human beings kind makes N mistake(s) ... 。

            ...

SQL Commands

DELETE。GROUP BY。INSERT。SELECT。UPDATE。, ... 。

Remark: The following SQL statement is an imaginary statement to allocate our Earth planet's current location。

SELECT Earth_current_location_at_present from Table1, Table2, Table3, Table4

WHERE

Orbiter1.Table1.ParallelTime1 = Orbiter2.Table2.Parallel2

AND

Orbiter3.Table3.ParallelTime3 = Orbiter4.Table4.ParallelTime4

GROUP BY 24mm_natural_time。

...

Also see: SQL.htm。 In 2008, IFF Oracle DB, 6 recommended books are Oracle Database 11g New Features, Oracle Database 11g DBA Handbook, Oracle Automatic Storage Management, Oracle Database 11g SQL, Oracle Database AJAX & PHP Web Development, and Oracle Database 11g PL/SQL Programming, also see: www.oraclepressbooks.com。

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