Database Principles Question Answer!! Rush 200

Answer: First Paradigm.

Let me briefly introduce you to the definition of one-two-three paradigms.

The premise of satisfying the second normal is satisfying the first normal form, the premise of satisfying the third normal form is satisfying the second normal form, and so on There are a total of 6 levels of paradigms. But the 123-level paradigm is commonly used.

The first normal form is the basic requirement that relational databases must meet, and a database that does not meet the first normal form is not a relational database.

The so-called first normal is that each column of the database is an inseparable basic data item, (for example, each record is not repeated, but the value of each column is repeated, because the relationship between course and major is many-to-many) There can be no multiple values in the same column, and an attribute in the entity cannot have multiple values or duplicate values. (For example, a course number corresponds to a course name.)

The second normal formula: the instance or row in the database table must be uniquely identified (that is, it is required to have a primary key, for example, a sequence is used to generate an id

In the Employees table, the employee code, department code, and other personal information of the employee are stored, but cannot contain field columns such as department name or address).

After reading this, I believe you will quickly understand why the question you are asking is the first paradigm. Simply storing the description of an entity, regardless of the primary key or the relationship with other tables, is the minimum requirement for a relational database. First Paradigm.

First Paradigm. This seems to be an example of the first paradigm in the course, you just read the book and understand more

When I first started learning paradigms, I was just as confused as you were.

God rewards hard work, and now it's clear about the database notes.

Set (10+x) pieces.

10+x)*(80-2x)=1200.

800-20x+80x-2x*x=1200.

x*x-30x+200=0

x-20)*(x-10)=0;

x1=20;x2=10.

x1 does not fit the topic (unit price 40 yuan), abandoned;

Bought 10 + 10 = 20 pieces.

(1) The second normal form has a transitive dependence (student number, department number, department name), so it is not the third normal form.

2) There are function dependencies: student number name, student number class, class department, department head, class counselor. According to the function dependency, there is a transitive dependence, so it is not a third normal.

Broken down into (student number, name, class), (class, counselor, department), (department, department chair).