SQL general     Last updated on 2013/2557 12 17, a full moon day;

Also see: Command; oracle; SQL.htm;

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 e.g. 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 vs. 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, e.g. abc CONTAINER . efg DATABASE . ijk TABLE . xyz COLUMN;

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) ... ;

Remark: The following SQL statement is an imaginary statement to allocate our Earth planet's current location, and notice that this query is not 2,3 dimensional, 2 vice versa 3; SQL Commands e.g. DELETE, GROUP BY, INSERT, SELECT, UPDATE, ... ;

SELECT Earth_current_location_at_present from Table1, Table2, Table3, Table4
Orbiter1.Table1.ParallelTime1 = Orbiter2.Table2.Parallel2
Orbiter3.Table3.ParallelTime3 = Orbiter4.Table4.ParallelTime4
GROUP BY 24mm_natural_time;

In 2013/2557, IFF Oracle Database 12c, also see: ADR, PGA, SGA, ... ;

declare, begin, (execute immediate, for, loop, using), end, ... ;

Keyword e.g. doko WHERE "using" might be for Microsoft's BASIC; "loop" means kuru kuru WHILE logic flows until done; for, common among programming languages; "execute immediate" is new in Oracle Database 12c ... ;

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;