Lecture 1. Monday, August 25, 2014

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1 Lecture 1 Monday, August 25, 2014

2 What is a database? General definition: An organized collection of information. 1

3 Different Types of Databases Flat file o A one-table database o Usually loaded into a multi-dimensional array by the application, manipulated, and saved back into the file o More difficult to search, insert, remove, or update records o Examples Plain text Common types CSV, tab-delimited Custom formats Developer creates a syntax of delimiters 2

4 Different Types of Databases Spreadsheets o A one-table database to most o Can be extended to be a limited relational database using functions like VLOOKUP o The average person can create and manage them without needing to know any programming o Easier to query using built-in tools, like PivotTables 3

5 Relational o o o o o Different Types of Databases Multiple tables Tables are related by linking together ( joining ) common fields Every table in a related database should somehow be related This is the type of database of class will focus on Relational database platforms MySQL o Freely available o Previously owned by SUN, later purchased by Oracle Oracle o Expensive to license o Mostly used by large organizations SQLite o Free, open source o Does not require a server/background process to run on or process anything o Stored in an individual, portable file o Frequently used on mobile devices and desktop applications 4

6 Different Types of Databases Relational (cont.) o Relational database platforms MySQL o Freely available o Previously owned by SUN, later purchased by Oracle Oracle o Expensive to license o Mostly used by large organizations SQLite o Free, open source o Does not require a server/background process to run or process anything o Stored in an individual, portable file o Frequently used on mobile devices and desktop applications 5

7 Basic Structure On a server/machine is the database management system (DBMS) Each DMBS contains one or more databases Each database contains one or more tables Each table contains one or more columns, called fields Each table contains rows, called records 6

8 Basic Structure Tables are just one object that can be found in a database Other types of objects include views, functions, procedures, and triggers we will talk about these later in the course 7

9 Basic Structure Besides managing data, some functions include: o Validation o Synchronization o Security 8

10 Table Structure Tables are made up of several columns/fields Like variables in our programming languages, each variable is assigned a type Types includes integers, char, float, etc. Also like variables in our programming languages, types that do not match up correctly will break your programs 9

11 Example: Bad Types One of our vendors gives this error message on one of it s screens CompanyName.Data.DbProviderException: Arithmetic overflow error for data type smallmoney, value = ! 10

12 Example: Bad Types The specific error message is an arithmetic overflow on a field with the variable type smallmoney, a variable type in Microsoft SQL Server, in which they are trying to store the number 421,223 smallmoney is a datatype that holds four bytes, which may lead one to assume it can hold between 0 and 2 8*4, or 4,294,967,296 BUT smallmoney o Reserves four digits as decimal places o Allows for negative numbers when not unsigned Thus, smallmoney s range of values is -214, and +214,

13 Example: Bad Types Does 421,223 fall within -214, and +214, ? NO Database systems may handle arithmetic overflow errors in one of two ways: o Give an error, and the program dies (as in this example, although the error message should have been more graceful ) o Truncate to the minimum/maximum value allows If strict SQL mode is on, the first method is used; if no restrictive modes are enabled (as dilbert is configured), the second method is used 12

14 Example: Bad Types Example 1 TINYINT o You have a TINYINT field, which hold 1 byte of data (up to 256) o You attempt to insert the number 395 o It will lower your number to 256, the maximum allowed in that field Example 2 VARCHAR o You have a VARCHAR field with 50 bytes/characters set as the length o You attempt to insert text of length 60 o It will truncate the last 10 characters from the string and use the first 50 In both of these cases, a warning will appear on dilbert, as strict SQL mode is not enabled 13

15 SQL SQL (Structured Query Language) is used universally by database management systems to perform all operations almost 14

16 SQL SQL commands (called queries) that manipulate data are generally, with some slight differences with more advanced querying, the same across database platforms: o SELECT * FROM mytable WHERE myfield = 'myvalue';! o INSERT INTO mytable (myfield) VALUES ('myvalue');! o DELETE * FROM mytable WHERE myfield = 'myvalue';! o UPDATE mytable SET myfield = 'mynewvalue' WHERE myfield = 'myoldvalue';! All of these work across Oracle, SQLite, MySQL, etc. 15

17 SQL However, commands that manage the DBMS may vary Example 1: TO get a list of tables in a database o MySQL: SHOW TABLES;! o SQLite:.tables! o Oracle: SELECT table_name FROM all_tables;! Example 2: To see the fields contained in a particular table: o MySQL and Oracle: DESCRIBE mytable;! o SQLite:.schema mytable! 16

Information Systems Engineering. SQL Structured Query Language DDL Data Definition (sub)language

Information Systems Engineering SQL Structured Query Language DDL Data Definition (sub)language 1 SQL Standard Language for the Definition, Querying and Manipulation of Relational Databases on DBMSs Its