Oracle difference projection selection intersection join description

 

 

There are similar questions in OCP 007:

 

Q: 141 evaluate this SQL statement:

Selecte. employee_id, E. last_name, E. department_id, D. department_name

From employees e, departments d

Where E. department_id = D. department_id;

 

In the statement, which capabilities of a SELECT statement are running med?

A. Selection, projection, join

B. Difference, projection, join

C. Selection, intersection, join

D. intersection, projection, join

E. Difference, projection, product

 

The answer here is. Let's take a look at the meanings of these terms:

 

Selection: query, select. Query some rows from the table.

Intersection: intersection. Two or more tables are joined to the common part.

Projection: Join and projection. Some columns are queried from the table.

Difference: difference set, two tables or different parts after multi-Table Association

Join: Join. This is described in my previous blog.

 

Join join: Internal join, external join, and self-join. The above question can be understood as internal join. By default, join is inner join, for external connections, you must specify the related keywords (left/right/full outer join) or symbols (+ ).

 

Detailed description of Oracle table connection (internal/external/self-connection)

Http://blog.csdn.net/tianlesoftware/article/details/5795896

 

 

 

 

 

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------- Add a group to describe the relationship between Oracle tablespace and data files in the remarks section. Otherwise, reject the application ----

Dba1 group: 62697716 (full); dba2 group: 62697977 (full) dba3 group: 62697850 (full)

Super DBA group: 63306533 (full); dba4 group: 83829929 dba5 group: 142216823

Dba6 group: 158654907 dba7 group: 172855474 dba8 group: 102954821