MySQL. Rheinisch-Westfälische Technische Hochschule Aachen Data Management and Data Exploration Group Univ.-Prof. Dr. rer. nat.

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1 Rheinisch-Westfälische Technische Hochschule Aachen Data Management and Data Exploration Group Univ.-Prof. Dr. rer. nat. Thomas Seidl Pro Seminar MySQL Student: Mohamed El Sherif June 2012 Supervision: Univ.-Prof. Dr. rer. nat. Thomas Seidl Dipl. Ing. Marwan Hassani

3 I hereby certify that I have written this paper independently and used nothing other than the stated sources and aids. Aachen, July 20, 2012

5 Contents 1 Introduction 3 2 Designing a bookstore search engine Creating database tables Creating database queries MySQL Workbench 9 4 Storage Engines Transaction Locks Examples of storage engines InnoDB MyISAM Comparison of storage engines Summary and Outlook 15 Bibliography 17 List of Abbreviations 17 Index 19 v

7 Abstract This paper discusses the syntax of MySQL and the MySQL Workbench designer tool used to communicate with a server storing data. It demonstrates the creation of a database using MySQL Workbench and shows how a query can be formulated to retrieve data from that database. Moreover, it illustrates the term 'storage engine' that MySQL provides and gives an overview of the dierent storage engines that MySQL oers. 1

8 2

Chapter 1 Introduction MySQL is one of the most popular open source RDBMS (Relational Database Management System) in the market and is owned by Oracle Corporation.

9 Chapter 1 Introduction MySQL is one of the most popular open source RDBMS (Relational Database Management System) in the market and is owned by Oracle Corporation. An RDBMS organizes data in the form of tables. A table consists of columns and rows and is a collection of related data entries. The table representation of the data is also a convenient way to express, understand and analyze the data. Creating tables and editing data in a database is usually performed using the programming language 'SQL'. 'SQL' stands for Structured Query Language, which is the default programming language when communicating with a server in an RDBMS. A common scenario when communicating with a web server that uses an RDBMS to manage its database is shown in Figure 1.1. Figure 1.1: A network of clients with a database access through a web server 3

10 4 Kapitel 1. Introduction A client sends a query to a server which then sends it to the RDBMS application. The RDBMS accesses the database, executes the query on its data then returns the answer for the query to the client. Usually multiple clients want to access the same database at the same time and want to have a fast response time. An RDBMS's responsibility is provision of clients with the desired answers of their queries in as little time as possible.

11 Chapter 2 Designing a bookstore search engine In this chapter, we will discuss how to manage a bookstore search engine with the help of MySQL. To do so, we will demonstrate some MySQL code for creating tables and then show how to initiate certain queries. A Query is the main mechanism for retrieving information from a database; it consists of a series of questions to the database in a predened format. MySQL, as well as many other RDBMSs use SQL as the standard query format. 2.1 Creating database tables 1 CREATE TABLE Book 2 ( BookID INT NOT NULL AUTO_INCREMENT, 3 T i t l e VARCHAR(45) NULL, 4 AuthorID INT NULL, 5 Publisher VARCHAR(45) NULL, 6 ISBN VARCHAR( 4 5) NULL, 7 PRIMARY KEY ( BookID ), 8 FOREIGN KEY ( AuthorID ) REFERENCES Author ( AuthorID ) ) 9 Engine = InnoDB ; In the rst line of the above code, we created a table in the database. In the rest of the lines we added some attributes to the table, so that any book in our database contains all these attributes. In line 8 we add a Foreign Key Constraint which ensures that our 'AuthorID' is actually stored in the table 'Author'. In this line we assume we have already added a table called 'Author' 5

12 6 Kapitel 2. Designing a bookstore search engine with an attribute named 'AuthorID'. The last line of this code is optional, since 'InnoDB' storage engine is the default storage engine in MySQL 5.6.[4] Hence, omitting the last line from the code would result in the storage engine being set as the default one.(further information on storage engines is given in Chapter 4) We added the optional 'AUTO_INCREMENT' ag when adding the attribute 'BookID', to ensure that a unique ID is created for every book automatically.[5] We also set our primary key to be the 'BookID' attribute. Most storage engines assign a hidden primary key if you do not assign one explicitly.[4] This code looks very similar to the code in other RDBMSs using SQL as the query format. We ll the 'Book' table as shown in Table 2.1. Similarly, Book BookID Title AuthorID Publisher ISBN 1 Harry Potter and the 1 Bloomsbury 2223 Philosopher's Stone 2 Harry Potter and the 1 Bloomsbury 2224 Chamber of Secrets 3 Harry Potter and the 1 Bloomsbury 2225 Prisoner of Azkaban 4 Twilight 2 HarperCollins 2228 Table 2.1: Table of Books we add two more tables for publishers and authors, where we store more information related to each of them. We ll the two tables as shown in Table 2.2 and Table 2.3. Author AuthorID First Last Country 1 J.K. Rowling UK 2 Max Mustermann DEU 3 Moritz Mustermann DEU Table 2.2: Table of Authors

13 2.2. Creating database queries 7 Publisher PublisherName Address Country Bloomsbury 34 oxford street,34502 UK HarperCollins 35 oxford street,34502 UK Table 2.3: Table of Publishers 2.2 Creating database queries A simple Query would be a simple question to the database that requests the rst two books that are written by "Rowling", published by "Bloomsbury" and containing "Harry Potter" in their title. The answer of this query should return the rst two books with their corresponding author that satisfy the requirements given. 1 SELECT Book. BookID, Book. T i t l e, Author. F i r s t, Author. Last 2 FROM Book, Publisher, Author 3 WHERE Book. Publisher = Publisher. PublisherName 4 AND Book. AuthorID = Author. AuthorID 5 AND Author. Last = ' Rowling ' AND Book. T i t l e LIKE '%Harry Potter%' 6 AND Publisher. PublisherName=' Bloomsbury ' 7 Limit 2 ; The SELECT keyword tells the database which columns should be received in the answer. The FROM keyword indicates which tables should be accessed to retrieve the data that is asked for. The WHERE keyword restricts the answer to only the rows that fulll all the conditions specied in the WHERE clause. The LIMIT keyword limits the answer to a certain number of rows. It is a keyword that is used in MySQL and a few other RDBMSs but is not a Standard SQL instruction.[5] SELECT, FROM and WHERE Keywords are part of the SQL Standard and are used in almost every RDBMS with SQL as its standard query format. After further examination of the query, one might recognize that the 'Publisher' table is redundant; it appears unnecessary to access the table at all. Accessing fewer tables almost always results in faster query processing time, which will result in a faster answer to the query. A 'NATURAL JOIN', allows for tables to be matched on common column names without explicitly naming the columns. In our example, we have the attribute 'AuthorID' that is stored in both tables 'Book' and 'Author', and

14 8 Kapitel 2. Designing a bookstore search engine that should match two rows together if, and only if, the 'AuthorID' of both tables is the same. 'Concat' is a predened function in MySQL, which is used to concatenate two or more strings to form a single string. In our example, we concatenate the authors' rst and last names together with a space in between to form the authors full name. After removing the 'Publisher' table and using the 'NATURAL JOIN' keyword, which joins the two tables 'Book' and 'Author' on 'AuthorID', we have a more simplied query which will take less time to be computed than the rst one. By adding a new column using the function concat, we are able to view the authors full name, making our answer clearer. We also make our query more readable by adding aliases to the tables. Aliases are usually smaller alternate names that are given to tables with long names. 1 SELECT b. BookID, b. T i t l e, Concat ( a. F i r s t, ' ', a. Last ) AS ' Author Name ' 2 FROM Book b NATURAL JOIN Author a 3 WHERE a. Last =' Rowling ' AND b. T i t l e LIKE '%Harry Potter%' AND 4 b. Publisher=' Bloomsbury ' 5 Limit 2 ; The previous query would result in the answer shown in Table 2.4. Answer BookID Title Author Name 1 Harry Potter and the Philosopher's Stone J.K. Rowling 2 Harry Potter and the Chamber of Secrets J.K. Rowling Table 2.4: Answer of the Query After looking at dierent queries, it is clear that the fewer tables the faster the processing time. Thus, it is important to try to minimize the number of tables used in a query. Writing readable queries is also important so the code is better understood by subsequent developers other than the author of the code.

Chapter 3 MySQL Workbench MySQL Workbench is a visual database management tool that is useful for database architects, developers and database administrators.

15 Chapter 3 MySQL Workbench MySQL Workbench is a visual database management tool that is useful for database architects, developers and database administrators. It is mainly divided into three sections: SQL Development, Data Modeling, and Server Administration. In this paper, SQL Development is used to test the SQL Code stated in the prior chapter (Chapter 2). Every operation that can be done in the Workbench can also be done in the command line of MySQL, which looks exactly the same as the usual command line in other programs. Figure 3.1 can be seen in the Home Screen of MySQL Workbench. Figure 3.1: Home Screen of MySQL Workbench After choosing which database one wants to connect to, one can then easily begin to add tables, edit data and execute queries in a user interface fashion. Our example from the previous chapter in Workbench would look like Figure

Triggers and indexes are not discussed in this paper but are essential properties of a table.

16 10 Kapitel 3. MySQL Workbench Figure 3.2: A screen shot of the Database used in Chapter 2 The tree view on the left, shows each table and its corresponding columns, indexes, foreign keys and triggers. Triggers and indexes are not discussed in this paper but are essential properties of a table. A highly valuable feature of the Workbench is the Data Modeling section, which allows users to visualize stored tables in a database. It is exceedingly convenient to have a graphic visual of the tables in order to be able to easily observe how everything is connected. Our Example can be modeled in an EER Model as shown in Figure 3.3. Figure 3.3: A screen shot of an EER-Model of the Database used in Chapter 2

17 Chapter 4 Storage Engines MySQL can store the data using dierent storage engines, each oering different features. Each storage engine has dierent strengths and weaknesses. MySQL oers a variety of storage engines that can be used in dierent databases. One can even use dierent storage engines in the same database for dierent tables.[4] This characteristic of MySQL makes it very exible for database administrators to manage various data in distinct tables according to dierent requirements and usage scenarios. This can reduce a lot of overhead and help in speeding the overall system, as opposed to using only one storage engine for the whole database. MySQL also oers the ability to implement a whole new custom storage engine for any specic application.[4] The great abstraction of how the data is stored from the rest of the MySQL architecture has made MySQL the preferred choice over a lot of other RDBMSs. Most RDBMSs, including some of the popular commercial ones, contain only one storage engine.[1] We will introduce a few denitions such that we can show the dierences among the various storage engines that MySQL oers Transaction A transaction is a collection of operations that are combined in one statement. This statement is either fully executed or not executed at all. A transaction must be atomic, consistent, isolated and durable. These four properties are often referred to as the ACID properties of a transaction. Atomicity demands that SQL-requests in a transaction are either all completed or all aborted.[2] 11

18 12 Kapitel 4. Storage Engines Consistency provides that a transaction brings the database from a valid state to another valid state. A state is valid, when it does not violate any integrity constraints.[2] Isolation ensures that data for a transaction T1 must not be available to other transaction T2 until T1 is either committed or rolled back.[2] Durability means that after a transaction is committed, the resulting changes in the database are stored permanently even if there was a database crash right after.[2] Locks Locking is used in databases to prevent multiple users accessing data concurrently in order not to invalidate or corrupt the data. The two most used locking strategies in RDBMSs are row-locks and table-locks.[2] When table locks are used and a 'write operation' is about to happen in a table, the entire table will be locked until the operation completes. Row-locks are more exible than table-locks. They lock only the rows that are to be written(updated,removed,added). This speeds up the process of writing to a table, when there is a lot of 'write operations' simultaneously, as opposed to locking the whole table for one 'write operation'. However row-locks produce a lot more overhead than tablelocks. [2] 4.1 Examples of storage engines InnoDB One of the most used storage engines in MySQL is the InnoDB storage engine, which is the default storage engine beginning from MySQL version 5.5.[4] InnoDB is one of the few storage engines that supports transactions and it uses row locking for simultaneously editing values in a database.[3] Thus, it would be extremely fast to write dierent values simultaneously in a InnoDB table, without worrying about data inconsistency. InnoDB stores the data physically on disk according to the primary key. This speeds up queries accessing the primary key.[4] In the bookstore example of Chapter 2, we used InnoDB when creating the table 'Book'. We choose this engine because transaction safe engines keep the data consistent and will not damage the data if a sudden crash occurs.

19 4.1. Examples of storage engines MyISAM MyISAM was the default storage engine for previous versions of MySQL until version 5.5.[4] It is extremely fast in reading data. If constant inserting and updating data is a requirement for an application then using MyISAM would not be ideal. The 'Publisher' table in the bookstore example of Chapter 2 had MyISAM as its storage engine. The reason for that is that publishers are rarely changed, and thus it will be an advantage to read data faster in that table. Moreover, MyISAM does not support transactions which causes poor data integrity and weak crash recovery. Crash recovery,which is the process that has to be done after a sudden crash of the database to ensure data integrity and data validity, has to be done in this case manually and can take a lot of time.[4] Comparison of storage engines Storage- Engine Transactions Locking Granularities Important Usage InnoDB Yes Row Lock transactionprocessing capability MyISAM No Table Locks SELECT,INSERT and load large amount of data Memory No Table Locks concurrent calculations,static lookups Archive No Row Locks logging,total analysis Storage Limits 64TB 256TB. RAM None Table 4.1: Summary of some of MySQL storage engines Table 4.1 demonstrates the dierences between some of MySQL's storage engines that are widely used. Beside InnoDB and MyISAM, mentioned above, there are Memory and Archive storage engines that are also well known but not as popular as the ones previously mentioned. There are other storage engines that come by default when installing MySQL, but their details are not essential for this paper. For further research on storage engines, check the MySQL reference manual[4].

20 14 Kapitel 4. Storage Engines

21 Chapter 5 Summary and Outlook There is an increasing need for prompt and ecient data management. In depth understanding of the RDBMS one will use, is essential to how procient the overall system will function. Experienced database administrators must be able to tune database servers to their limits. With the growing varieties and features currently in the market, it is not always easy to nd the best approach to solve a specic problem. As MySQL is one of the most used open source RDBMSs in the market, the community of people using the software on the internet is vast, thus making it relatively accessible to obtain online, a most suitable solution to a problem that one is faced with. 15

22 16 Kapitel 5. Summary and Outlook

23 List of Abbreviations SQL Structured Query Language RDBMS Relational Database Management System EER Enhanced Entity-Relationship Model 17

24 18 LIST OF ABBREVIATIONS

25 Bibliography [1] [2] Baron Shwartz, Peter Zaitsev. High Performanca MySQL. O'Reilly, [3] Mariella Di Giacomo. Mysql: Lessons learned on a digital library. Software, IEEE, [4] MySQL Developers. MySQL 5.6 Reference Manual, [5] Russel J.T. Dyer, Lars Schulten. MySQL In A Nutshell. O'Reilly,

Proseminar. Mohamed El Sherif

Proseminar. Mohamed El Sherif Proseminar Mohamed El Sherif Rheinisch-Westfälische Technische Hochschule Aachen Data Management and Data Exploration Group Univ.-Prof. Dr. rer. nat. Thomas Seidl Supervision: Dipl. Ing. Marwan Hassani