Database relational database Database management system Access Sen Zhang What is a databse? • A database is a collection of information stored on a computer in a systematic and structured way, which should facilitate information retrieval. What is database management system? • The tool that can process database is called database management system ( not a hammer, an integrated software) Relational database and relational database management system • Relational database is the database where data are structured as relations (tables). • Correspondingly, the database management system is called RDBMS. • Database application cares about not only keeping track of information, but also retrieving information. • So, to facilitate information retrieval, a database application has to consider how to save data in some well defined structures. Why structured? • Think about how to put your books on shelves. • Fast retrieval • But slow down storing • It is worth of the effort • Database application is meaningful when you need to save data and dynamically search data as well as derive new data, more powerful than Excel. • It is especially useful when the application concerns about huge amount of information. • One example, all transactions of Walmart. • How does Walmart maintain all customer transactions? • How does walmart maintain all information about different kinds merchandise? • Why maintain database? • Why you maintain your house? • Do you need them later? If yes, then you need. • You can find out other examples • Excel organizes things in worksheets. – An Excel Worksheet looks like a huge “table”. – However, in the stricter sense, a Worksheet is not a table. Why? • From format point of view, it looks like a table • From structure point of view, it is not treated like a table. Is Excel the right tool for database? – To certain extend, an Excel “workbook” can be treated as a very rudimentary “database”, but • A workbook is – structured at visualization level and data structure level – but unstructured at semantic level. » Each cell is independent from the cells in the same column. – Therefore is not appropriate for relational database, not the right data. • And Excel has not designed as a tool to process database, – So, it is not a right tool. Access is the right tool – In Microsoft office suite, It is Access that is the tool to process database stored in a kind of specially defined data file. – It requires data to be specially organized. • Excel does not impose rigid structure requirements to data in individual cells. • Excel is not good at handling massive amounts of data. • Excel does not support queries from different “tables” (actually, tables in Excel are different from the Access’s tables!) • It is the Access where tables are used in the real sense (It might sound difficult to understand at this moment, but it will be clear at the end of the lecture) . • We will see the differences. Why Access is needed? • How do you maintain information of 5000 students, 500 different classes and class enrollment for Oneonta college? Can you use Excel Worksheets? • You cannot simply use Excel to accomplish the goal for many reasons: – different offices may keep different Excel Workbooks for different purposes. – redundant information will be stored, which easily causes inconsistencies across the campus. – the information changes all the time, – and a large number of different reports might be requested by different people. – It is tedious and actually impossible to create various excel sheets to maintain different information separately. – …. Solution is to use database • We need a better way, a centralized way to store data, organize data, retrieve data, and display data. • A database is usually a collection of centralized and organized data (or tables). • Database is managed by database management system. • Microsoft Access is a powerful program to create and manage your databases. • Access is a database management system, and more precisely, a relational database management system. • In a relational database, everything will be organized into tables. (a table = a relation). What is Microsoft Access? • It has many built in features to assist you in constructing and viewing your information. • Access is much more involved and is a more genuine database application than other programs such as – Microsoft Word(good at documentation), – Excel (simple spreadsheet good at small amount of data.) – PowerPoint (presentation) – FrontPage (website development). Define some key Access terminology Field vs. Field value. • Field – A single characteristic or attribute of a person, place, object, event, or idea. • Field value – The specific value, or content, of a field is called the field value. Record and table • Record – A set of related field values. – a Customer may have name, age, birthday, SSN etc. • Table – A collection of records that identify a category of data, such as Customers, Orders, or Inventory. Illustration of fields, records and a table A Primary key • A primary key is a field, or a collection of fields, whose values uniquely identify each record in a table. – The primary key uniquely identifies a record in the table. In other words, a primary key allows user to distinguish one record from another in the same table. – In Access, a table usually has a field, or a collection of fields to be designated as the primary key. (Not a must, but usually we do.) Relational database and keys • A relational database is a collection of tables that are related to one another based on a common field. • When the primary key of one table is represented in a second table to form a relationship, it is called a foreign key. Relating tables using a common field Relational database? • Every piece of information will be stored in relations, i.e. tables. • For example, student table looks like: Student id name year status A23232 john 1988 good A23355 john 1976 good A34333 kathy 1979 good Relational databse? Course table Course id Course instructor credit name c900 computing sen 3 c905 database sen 3 Relational databse? Enrollment table sequence Studentid courseid status 1 a23232 c900 n 2 a34333 c905 w Relational database? Student id name year status A23232 john 1988 good A23355 john 1976 good A34333 kathy 1979 good Course id Couse name instructor credit c900 computing sen 3 c905 database sen 3 sequence studentid courseid status 1 a23232 c900 n 2 a34333 c905 w Several Terminologies • A database is a collection of related information. • An object is a member in the database such as a table, query, form, or macro. • A table is a grouping of related data organized in fields (columns) and records (rows) on a datasheet. By using a common field in two tables, the data can be combined. Many tables can be stored in a single database. • A field is a column on a datasheet and defines a data type for a set of values in a table. For a mailing list table might include fields for first name, last name, address, city, state, zip code, and telephone number. • A record in a row on a datasheet and is a set of values defined by fields. In a mailing list table, each record would contain the data for one person as specified by the intersecting fields. • Design View provides the tools for creating fields in a table. • Datasheet View allows you to update, edit, and delete in formation from a table. More detailed Breakdown of tables Hierarchy that Microsoft Access uses • Table:A table is a collection of data about a specific topic. There can be multiple tables in a database. Example #1) Students Example #2) enrollments • Field:Fields are the different categories within a Table. Tables usually contain multiple fields. Example #1) Student LastName Example #2) Student FirstName • Datatypes:Datatypes are the properties of each field. A field only has 1 datatype. FieldName) Student LastName Datatype) Text • Values: for example a student lastname could be herbert. Blank Access database • Unlike Word documents, Excel worksheets, and Power Point presentations, you must save an Access database before you start working on it. After selecting "Blank Access database", you will first be prompted to specify a location and a name for the database. Database Window • The Database Window organizes all of the objects in the database. The default tables listing provides links for creating tables and will list all of the tables in the database when they have been added. Design View • Design View customizes the fields in the database so that data can be entered. Datasheet View • The datasheet allows you to enter data into the database Access database wizards, pages, and projects • Access' wizards and layout are existing database structures that only need data input. Select a database type and click OK. Name the database on the next screen. Forms A form is nothing more than a graphical representation of a table. You can add, update, delete records in your table by using a form. NOTE: Although a form can be named different from a table, they both still manipulate the same information and the same exact data. Hence, if you change a record in a form, it will be changed in the table also. Actually, a form and a datasheet are simply different views of the same table. Form view vs. Datasheet view A form is very good to use when you have numerous fields in a table. This way you can see all the fields in one screen, whereas if you were in the table view (datasheet) you would have to keep scrolling horizontally to get the field you desire. A form is also very good to use when you have numerous records in table. This way you can concentrate on single record in one screen, whereas if you were in the table view (datasheet) you would have to keep scrolling vertically to get the record you desire. What is an Access query? • If you want to see just a portion of the data in a table you can create a query. • A query is a question you ask about the data stored in a database table. • Access responds by displaying the data according to your question. – For example, if you ask to see all the customers from New York, the response would be to display only the records whose state field matches with NY Open an existing query and create new queries • You can open an existing query by clicking Queries on the Objects bar and then selecting the query you want to open. • You can also create your own queries by clicking New on the Database window. • To create a new query, you can use the Simple Query Wizard, which will bring you through the selections you want for your query. Navigating a query and sorting the results • When you run and get the results of your query, you can reorganize the data by sorting the datasheet in either ascending or descending order. – Click the pointer anywhere in the column you wish to sort – Click the Sort Ascending or Sort Descending buttons on the Query Datasheet toolbar to sort the results in the desired sequence • You can navigate through the records by using the navigation buttons on the Navigations toolbar. Reports • A report is an effective way to present your data in a printed format. Because you have control over the size and appearance of everything on a report, you can display the information the way you want to see it.
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