Shulou(Shulou.com)05/31 Report--

This article mainly introduces "how to quickly grasp the principle of database". In daily operation, I believe that many people have doubts about how to quickly grasp the principle of database. The editor consulted all kinds of materials and sorted out simple and easy-to-use operation methods. I hope it will be helpful for you to answer the doubt of "how to quickly master the principle of database"! Next, please follow the editor to study!

The databases we are familiar with are generally relational databases, such as Oracle, Sql Server, DB2, Mysql and so on. Oracle is generally used in telecom companies, and Sql Server can find it in small and medium-sized enterprises or retail companies. DB2 generally works with IBM mainframes (such as OS390), which can only be used by high-end banks, while Mysql often shows its identity on Taobao and other websites because of its open source and support for highly available clusters.

When it comes to databases, the most basic thing is to find out the secret of its principle. We need to understand the basic characteristics of relational database, the syntax structure of SQL, as well as database programming technology, data security and protection mechanism.

Several familiar concepts are explained as follows

1. The third normal form 3NF, that is, the second normal form 2NF that does not have a transfer function dependency, and the second normal form is the first normal form 1NF in which all non-principal attributes of the table are functionally dependent on the candidate keywords. The first normal form is that the value at the intersection of each column and row in any given relation R is an inseparable basic element, that is, it does not contain the relationship of repeating groups or the nested structure.

2. Emurr diagram, which represents the relationship diagram of tables or entities, usually as the design of the relationship between tables, belongs to the category of static component diagram of UML language, and can list the details of each table field. Generally speaking, the forms we design should conform to the third normal form; www.walekan.com/kj/kjpp/1487

3. The join relation of the table (JOIN). The join relation between the tables is multiplied by Cartesian product, such as the product of the I column attribute value of R and the j column attribute of S in R X S. The connection is divided into inner connection and outer connection, and the outer connection is divided into left outer connection and right connection.

4. Common SQL statements:

Create database/table/PROCEDURE (create operation)

Select, insert,update,delete (add, delete, change and search)

Select col_name INTO var_name (variable assignment)

DROP database/table/PROCEDURE (delete operation)

DECLARE cursor_name CURSOR FOR (declare cursors)

OPEN cursor_name (open cursor)

FETCH cursor_name INTO var_name (cursor value)

Create Trigger mysql.customers After Insert (create trigger)

IF...THEN...ELSE (grammatical structure of conditional judgment)

At this point, the study on "how to quickly grasp the principle of database" is over. I hope to be able to solve everyone's doubts. The collocation of theory and practice can better help you learn, go and try it! If you want to continue to learn more related knowledge, please continue to follow the website, the editor will continue to work hard to bring you more practical articles!

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