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CSC 2720 Building Web Applications Database and SQL
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Database and DBMS Database – Structured collection of records or data Database Management System (DBMS) – Specialized software for managing databases Relational Database – A type of database in which data are organized as related tables Most widely used type of databases
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Advantages of using DBMS Efficient Data Access Support multiple users and Data Security Protect access to data in which only authorized users can access the data Concurrent Access Support mechanisms to allow multiple users to safely read/write the data. (e.g., record locking) Transaction Crash Recovery
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Advantages of using DBMS Standardized query language for defining and manipulating data Network accessible DBMS Web App (Java Servlet) Web App (PHP) Web App (ASP.NET) Stand alone App (Java / C++ / C ) Database Management Tools SQL
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Introduction to Relational Database Data are stored in tables (a.k.a. relations). ItemIDNamePriceQuantity 0123456Coffee4.50100 0222222Soy Milk4.4050 0142562Tea5.0040 Row / Record Column / Field / Attribute A table has a name. A field has a name and a type. Besides some standard types, different DBMS (e.g., Oracle and MySQL) may also have their own specific types.
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Characteristics of a Table A field is said to contain a null value when it contains nothing at all. When defining a table, we can set whether a field can contain a null value or not. Keys are special fields that serve a specific purpose within a table. A Primary key is a field (or combination of fields) that uniquely identifies a record within a table. A Foreign key is the field that is used to establish a relationship between a pair of tables.A foreign key has to be a primary key of another table. Row orders are not important.
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Structured Query Language (SQL) A standardized language that can be used to build, modify, maintain and manipulate a database SQL supported by different DBMS may vary slightly. With SQL, you can Create/delete a database Create/delete tables in a database Retrieve data from a database Insert new records in a database Delete records from a database Update records in a database
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SQL (con't) SQL is case insensitive Multiple statements are separated by semicolon Important commands for manipulating data SELECT - extracts data from a database table UPDATE - updates data in a database table DELETE - deletes data from a database table INSERT INTO - inserts new data into a database table Important commands for manipulating table CREATE TABLE - creates a new database table ALTER TABLE - alters (changes) a database table DROP TABLE - deletes a database table Examples: SQL Tutorial at W3Schools http://www.w3schools.com/sql/default.asp http://www.w3schools.com/sql/default.asp
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