Working with MySQL Database creation and MySQL

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1 Working with MySQL Database creation and MySQL MySQL is a database system, a database server. To interface with the MySQL server, you can use a client program or you can write a program or script with one of the popular programming languages (such as Perl) using an API (Application Programming Interface) to interface with the MySQL server. Login to neo.engr.smu.edu When you have your userid and password, login to mysql using the command: mysql umyuserid ppassword hcypher where myuserid and password are the userid and password given to you in class. You should see the prompt change to mysql. Getting Started with MySQL Use the SHOW statement to find out what databases currently exist on the server. Your account will typically come with two databases set up for you. The one you will use for your work is the one that starts with db<your name>. The test database is one for you to experiment with. mysql> SHOW DATABASES; Database dbsmith test The list of databases you see will be different based on your account. The test database is often provided as a workspace for users to try things out. The other database you see has been set up for you to use in the class. mysql>use test; This is how to tell MySQL which database will be the active one. mysql>show tables; shows all the tables in the database

2 Switch to your database. Use the USE command to tell MYSQL to use your other database? Q: How many tables are in your database? Creating a Table Tables are at the heart of your database. Creating the database is the easy part, but at this point it s empty, as SHOW TABLES will tell you: mysql> SHOW TABLES; Empty set (0.00 sec) The harder part is deciding what the structure of your database should be: what tables you will need and what columns will be in each of them. Use a CREATE TABLE statement to specify the layout of your table: mysql> CREATE TABLE pet (name VARCHAR(20), owner VARCHAR(20), -> species VARCHAR(20), sex CHAR(1), birth DATE, death DATE); VARCHAR is a good choice for the name, owner, and species columns because the column values will vary in length. The lengths of those columns need not all be the same, and need not be 20. You can pick any length from 1 to 255, whatever seems most reasonable to you. (If you make a poor choice and it turns out later that you need a longer field, MySQL provides an ALTER TABLE statement.) Several types of values can be chosen to represent sex in animal records, such as 'm' and 'f', or perhaps 'male' and 'female'. It s simplest to use the single characters 'm' and 'f'. The use of the DATE data type for the birth and death columns is a fairly obvious choice. Now that you have created a table, SHOW TABLES should produce some output: mysql> SHOW TABLES; Tables in menagerie pet

3 To verify that your table was created the way you expected, use a DESCRIBE statement: mysql> DESCRIBE pet; Field Type Null Key Default Extra name varchar(20) YES NULL owner varchar(20) YES NULL species varchar(20) YES NULL sex char(1) YES NULL birth date YES NULL death date YES NULL You can use DESCRIBE any time, for example, if you forget the names of the columns in your table or what types they have. Loading Data into a Table After creating your table, you need to populate it. The INSERT statement is useful for this. Suppose that your pet records can be described as shown here. (Observe that MySQL expects dates in 'YYYY-MM-DD' format; this may be different from what you are used to.) name owner species sex birth death fluffy harold cat f claws gwen cat m buffy harold dog f fang benny dog m When you want to add new records one at a time, the INSERT statement is useful. In its simplest form, you supply values for each column, in the order in which the columns were listed in the CREATE TABLE statement. Suppose that Diane gets a new hamster named Puffball. You could add a new record using an INSERT statement like this: mysql> INSERT INTO pet --> VALUES ('puffball','diane','hamster','f',' ',null); Note that string and date values are specified as quoted strings here. Also, with INSERT, you can insert NULL directly to represent a missing value.

4 Retrieving Information from a Table The SELECT statement is used to pull information from a table. The general form of the statement is: SELECT what_to_select FROM which_table WHERE conditions_to_satisfy; what_to_select indicates what you want to see. This can be a list of columns, or * to indicate all columns. which_table indicates the table from which you want to retrieve data. The WHERE clause is optional. If it s present, conditions_to_satisfy specifies conditions that rows must satisfy to qualify for retrieval. Selecting All Data The simplest form of SELECT retrieves everything from a table: mysql> SELECT * FROM pet; name owner species sex birth death fluffy harold cat f NULL claws gwen cat m NULL buffy harold dog f NULL fang benny dog m NULL bowser diane dog m chirpy gwen bird f NULL whistler gwen bird NULL NULL slim benny snake m NULL puffball diane hamster f NULL This form of SELECT is useful if you want to review your entire table, for example, after you ve just loaded it with your initial dataset. For example, you may happen to think that the birth date for Bowser doesn t seem quite right. Consulting your original pedigree papers, you find that the correct birth year should be 1989, not Changing and deleting data To change existing data, a common method is to use the UPDATE statement. When changing data, though, we need to be sure that we change the correct rows. In our example, there could be another book with the title America written by a different author. Since the key column isbn has only unique numbers and we know the ISBN number for the book that we want to change, we can use it to specify the row. UPDATE pet SET birth = ' ' WHERE name = 'bowser';

5 If we want to delete a row of data, we can use the DELETE statement. For instance, suppose that our fictitious bookstore has decided no longer to carry books by John Grisham. By first running a SELECT statement, we determine the identification number for the author to be Using this author identification number, we could enter the following: DELETE FROM pet WHERE name = 'bowser'; This statement deletes all rows from the table books for the name given.

6 do: Create a new table called users. How you structure it is up to you as long as you can retrieve userid and passwords to validate incoming users. Sample schema for users: lastname firstname gender username password varchar(12) varchar(12) char(1) varchar(8) varchar(8) When your table has been set up, use the DESCRIBE command to examine the table; Use the MYSQL INSERT command to insert at least 4 users into your USERS table. These four users should have the username harold benny gwen diane Examine your new data using the SELECT * command. What is the full command? Use the UPDATE command to change diane s password to dd123. What is the command? What is the command to show all the males in your USERS table?

7 MYSQL Commands Login: mysql umyuserid ppassword hcypher MYSQL System Commands mysql> SHOW DATABASES; Database dbsmith test Switch to a specific database; show tables mysql>use test; mysql>show tables; Examine table columns mysql> DESCRIBE pet; MYSQL Table Commands Create new table mysql> CREATE TABLE pet (name VARCHAR(20), owner VARCHAR(20), species VARCHAR(20), sex CHAR(1), birth DATE, death DATE); Insert Data mysql> INSERT INTO pet VALUES ('puffball','diane','hamster','f',' ',null); Retrieve (select) data from a table SELECT what_to_select FROM which_table WHERE conditions_to_satisfy; SELECT everything from a table mysql> SELECT * FROM pet;

8 Select only certain fields from all the data mysql> SELECT name, sex FROM pet; Select only certain fields based on criteria only cats mysql> SELECT name, owner, sex FROM pet WHERE species= cat ; Modify Data [UPDATE..SET..WHERE mysql> UPDATE pet SET birth = ' ' WHERE name = 'bowser'; Delete a row of data mysql> DELETE FROM pet WHERE name = 'bowser'; MySQL SQL Selectable Items VERSON() CURRENT_DATE USER() SHOW DATABASES; - Show the databases that exist on the server. SHOW TABLES; USE dbname - Use a specific database. LOAD DATA; DESCRIBE - Get information about a table's columns. Keywords DISTINCT ORDER BY - Set the order the output is displayed in. COUNT - Count rows in a table. Comparison Operators IS NULL IS NOT NULL LIKE m% - Items beginning with the letter m. NOT LIKE

9 REGEXP Select - table. EX: "SELECT VERSION(), CURRENT_DATE;" Syntax: <img> SELECT what FROM tablename WHERE conditions The SELECT condition allows selection of columns such as "colname1, colname2". The WHERE condition allows the selection of specific rows (items). EX: SELECT * FROM tablename Insert - Create tables Update - table Delete - table Index - Used to create or remove indexes for tables. Alter - Used for tables, allows the use of the "ALTER TABLE" command. Create - Make new database, table, or index. Drop - Remove database or table. Grant - Allows a user to give other users the privilege that they have. Used to grant access to databases or tables. References - Database or table. Reload - Have the database engine re-read the grant tables. Shutdown Process File - Can read and write files on the SQL server using "SELECT...INTO OUTFILE" or "LOAD DATA INFILE". Specific functions LOAD DATA INFILE Additional Commands OPTIMIZE TABLE - Used after many changes have been made to a table. ANALYZE TABLE - Analyze and store the table key distribution. FLUSH - Need RELOAD privilege to use this. This command flushes any unsaved buffers to permanent storage. Syntax: FLUSH flush_option [,flush_option] Options: o o HOSTS - Empty host cache table. LOGS - Close, then open all log files.

10 o PRIVILEGES - Reload privileges from the grant tables. o TABLES - Close all tables o STATUS - Used for debugging queries, it will clear status variables. KILL - Can kill a connection thread to the MySQL server. Requires the PROCESS privilege to kill processes that are not the user's processes. The command syntax is "KILL thread_id". SHOW (4.5.5) - Presents information about databases, tables, or columns. Options: o SHOW DATABASES - List databases o SHOW [OPEN] TABLES [FROM] databasename - List the tables in a database. o SHOW [FULL] COLUMNS FROM tbl_name [FROM db_name] [LIKE wild] - Show columns in a table. o SHOW FIELDS - A synonym for SHOW COLUMNS. Java Code: import java.util.*; import java.sql.*; public class JDBCMysql { public static void main (String [] args) { // the URL string that points to the server =cypher.engr.edu // and database = dbcoyle String url = "jdbc:mysql://cypher.engr.edu/dbcoyle"; // a query we want to feed the database String query = "SELECT * FROM UserTable"; try { // use the magic of REFLECTION to create an // instance of the com.mysql.jdbc.driver class Class.forName ("com.mysql.jdbc.driver"); // tell the DriverManager to connect to our database // called dbcoyle. More magic here: the DriverManager // will snoop around and find the Driver instance we // created in the previous statement. The DriverManager will // login for us Connection con = DriverManager.getConnection(url,"zorro","garcia"); System.out.println("Connection made!");

11 // from here on it's regular JDBC.. Statement stmt = con.createstatement (); ResultSet rs = stmt.executequery (query); System.out.println(rs ); rs.close(); stmt.close(); con.close(); // end try catch (SQLException ex) { System.out.println ("SQL Exception: " + ex.getmessage ()); // end catch SQLException catch (java.lang.exception ex) { System.out.println ("Exception: " + ex.getmessage ()); import javax.servlet.*; import javax.servlet.http.*; import java.sql.*; import java.io.*; import java.util.*; class JDBCServletTest extends HttpServlet { public void doget(httpservletrequest request, HttpServletResponse response) throws ServletException, IOException{ try { response.setcontenttype("text/html"); PrintWriter out = response.getwriter(); Class.forName("oracle.jdbc.driver.OracleDriver"); Connection conn = DriverManager.getConnection( "jdbc:oracle:thin:@dop.engr.smu.edu:1521:dop03", "mfonten", "mfonten123"); Statement stmt = conn.createstatement(); String doctype = "<!DOCTYPE HTML PUBLIC \"-//W3C//DTD HTML 4.0 " + "Transitional//EN\">\n";

12 out.println(doctype + "<HTML>\n" + "<HEAD><TITLE> JDBC Servlet Test </TITLE></HEAD>\n"+ "<BODY>"); String str = "Select * from student"; ResultSet rs = stmt.executequery(str); while (rs.next()){ String ret = rs.getstring(1); ret += " " + rs.getstring(2) + " "; ret += rs.getstring(3); out.println(ret); out.println("\n</body></html>"); conn.close(); out.close(); catch (Exception e) { e.printstacktrace();