This time is very busy, but I finally decided to write something to record this hot period. . .
It has also been developed for several years. There are several databases that have been designed. The experience value is constantly rising, but I always feel that there is something that I can't see the essence, the hierarchy, so I decided to focus on "database system" Introduction and "Data Structure", I want to learn the power of the theory, let my database understand more, learn, I will record some experience, share with time and space!
My learning environment is: WindowsXP, SQL Server2000 Development Edition with SP3A, Visualstudio2003 (C # and ASP.NET with C #).
Based on my current level, learning the database system from three aspects: 1. Design of the design specification and intervals of the study 2, the in-depth study of the SQL language, including the view, stored procedures 3, the database system itself
The following official start: well known, the current mainstream model of the database system is the relationship and object-oriented model, the layered and mesh models are in progressive phase, and the basic composition of the relational database is a two-dimensional table (TABLE), The two-dimensional table contains "type" and "value", "type" is also the column attributes we often say, also called fields, and "value", is our line (also called record The content is. The correlation between the tables and the table is what we usually say "relationship".
The database system uses the three-level mode structure (external mode SCHEMA, Mode External Schema, and internal mode Internal Schema) to be a database user's data view. It is the data form of the user who can be understood as SQL language. As a result, the data we want is extracted from each data sheet. Mode is a description of the logical structure and characteristics of all data in the database. It can be understood as the design of each table and the relational design of the table. It is directly related to the application design requirements. It is the architecture of the data store, the design of the design is directly affected. To the execution efficiency of the application. The internal mode is the storage method within the database system. For example, our data is stored in order storage or a linked list storage, press B-tree structure storage or by the Hash method storage, storage is encrypted, etc., this mode We don't want to pay attention, it It is the content of the database system designer to care.
Therefore, we have to care about the model and exterior mode, corresponding to the 1st and 2nd point I said above.
Relational database system is a database system that supports relational data models, and the relational model consists of a relational data structure, a relationship operation set, and a relationship integrity constraint. The relational data structure is a two-dimensional table, and the relationship operation usually includes: Select, Project, Connection (JOIN), Divide, and (Union), Diffance (Difference) ) Insert, delete, modifying the three integrity constraints of the UPDATE relationship include: entity integrity, reference integrity, and user-defined integrity.
Next is the SQL query language, the SQL language hides all the complex data operations, we only need to do what to do, design the corresponding SQL statement, how to do it is made up by the system.
SQL language is divided into four categories: data query, data manipulation, data definition, data control, where data queries are our most familiar SELECT, its group by statement, I like it, and I will count the statistics of the data. Below is an example of nesting SELECT: SELECT SNAME, SAGE FROM Student Where <(Sage) (Sage) (Sage) ") and sql's function is query : The learning and proficiency of student names and age SQL languages in the computer system is the focus of our database, and the design of the data table structure is interacting, what kind of data sheet is there. What kind of SQL statement will there be, the learning of these is mutually promoted, and the most experience accumulation is required. Based on its complexity, there is no more exploration here.
With the SQL language, you have to say a view, and the view is actually closely associated with the SELECT statement. It is actually equivalent to a virtual table. The execution view will see the corresponding back table SQL results.
By the way, the SQL Server 2000 provides complete SQL support and view support, executing SQL statements and views can be operated in the Enterprise Manager, or in the query analyzer, you can pass the corresponding in your own program. Interface operation.
(First, starting on October 14, 2004, updated on October 22, continuous update ...)
