12DatabaseProgramming-20151219摘要.pptx

12 Database Management 12 Database Management 12.1 An Introduction to Databases 12.2 Relational Databases and SQL 12.3 ADO.NET 12.1 An Introduction to Databases 1 Database Terminology A table is a rectangular array of data. Each column of the table, called a field, contains the same type of information. Each row, called a record, contains all the information about one entry in the database. In a phone books, there are fields for name, address, and phone number. Your entry in the phone book is a record. 2 Database Management Software (DBMS) Used to create databases Databases can contain one or more related tables Examples of DBMS include Access and SQL Server Create a DB named Studentmanagement.MDF which has 3 tables: students, courses, stu_courses 12.2 SQL Primary and Foreign Keys SQL Four SQL Requests The DataGrid Control Primary Keys A primary key is used to uniquely identify each record. Databases of student enrollments in a college usually use a field of Social Security numbers as the primary key. Why wouldnt names would not be a good choice as a primary key? Two or More Tables When a database contains two or more tables, the tables are usually related. For instance, the two tables Students and Stu_courses are related by their sno field. Notice that every entry in Stu_courses.sid appears uniquely in Students.sid and Students. sid is a primary key. We say that Stu_courses is a foreign key of Students. sid. Foreign Keys Foreign keys can be specified when a table is first created VB.NET will insist on the Rule of Referential Integrity. This Rule says that each value in the foreign key must also appear in the primary key of the other table. Join A foreign key allows VB.NET to link (or join) together two tables from a relational database When the two tables Students and stu_courses from Studentmanagement.MDF are joined based on the foreign key Stu_courses.sno, the result is … SQL Structured Query Language developed for use with relational databases Very power