Giải pháp thiết kế web động với PHP - p 32 pptx

GETTING STARTED WITH MYSQL 291 11. Click Add a new User, and repeat steps 4 through 8 to create a second user account called psread. This user will have much more restricted privileges, so when you get to step 7, check only the SELECT option. The password used for psread in the example files is K1y0mi$u. Creating a database table Now that you have a database and dedicated user accounts, you can begin creating tables. Lets begin by creating a table to hold the details of images, as shown in Figure 10-1. Before you can start entering data, you need to define the table structure. This involves deciding the following: • The name of the table • How many columns it will have • The name of each column • What type of data will be stored in each column • Whether the column must always have data in each field • Which column contains the tables primary key If you look at Figure 10-1, you can see that the table contains three columns: image_id (primary key), filename, and caption. Because it contains details of images, thats a good name to use for the table. Theres not much point in storing a filename without a caption, so every column must contain data. Great! Apart from the data type, all the decisions have been made. Ill explain the data types as we go along. Defining the images table These instructions show how to define a table in phpMyAdmin. If you prefer to use Navicat, SQLyog, or a different UI for MySQL, use the settings in Table 10-1. 1. Launch phpMyAdmin, if its not already open, and select phpsols from the Database drop- down menu in the left frame. Type the name of the new table (images) in the field labeled Create new table on database phpsols, and enter 3 as the Numb er of fields. (As mentioned before, phpMyAdmin refers to columns as fields. What it means is how many fields each record has.) Then click the Go button. 2. The next screen is where you define the table. Because the images table contains only three columns, the options for each column are listed vertically. When you define a table with more than three columns, the options are displayed horizontally. There are a lot of options, but not all of them need to be filled in. Table 10-1 lists the settings for the images table. Table 10-1. Settings for the images table Field Type Length/Values Attributes Null Index AUTO_INCREMENT image_id INT UNSIGNED Deselected PRIMARY Selected filename VARCHAR 25 Deselected caption VARCHAR 120 Deselected CHAPTER 10 292 The first column, image_id, is defined as type INT, which stands for integer. Its attribute is set to UNSIGNED, which means that only positive numbers are allowed. Its index is declared as PRIMARY, and the AUTO_INCREMENT check box is selected, so MySQL automatically inserts in this column the next available number (starting at 1) whenever a new record is inserted. The next column, filename, is defined as type VARCHAR with a length of 25. This means it accepts up to 25 characters of text. The final column, caption, is also VARCHAR with a length of 120, so it accepts up to 120 characters of text. The Null check box for all columns is deselected, so they must always contain something. However, that “something” can be as little as an empty string. Ill describe the column types in more detail in “Choosing the right column type in MySQL” later in this chapter. The following screenshot shows the options after they have been set in phpMyAdmin: 3. Toward the bottom of the screen is an option for Storage Engine. This determines the format used internally by MySQL to store the database files. MyISAM is the default storage engine in MySQL 3.23 through 5.1. However, it has been announced that an improved version of the InnoDB storage engine will become the default in MySQL 5.5. At the time of this writing, many Download from Wow! eBook <www.wowebook.com> GETTING STARTED WITH MYSQL 293 hosting companies dont support InnoDB or offer it only on premium hosting plans. Ill explain the differences between these storage engines in Chapter 16. In the meantime, use MyISAM. Converting from one storage engine to another is very simple. 4. When you have finished, click the Save button at the bottom of the screen. If you click Go instead of Save, phpMyAdmin adds an extra column for you to define. If this happens, give the new column a dummy name, and set the Type option to IN T. You can then delete the extra column by clicking the Delete icon (a red cross) in the relevant row in the Structu re table that appears in the next screen. 5. The next screen displays the SQL query that phpMyAdmin used to define the images table. Beneath that, youll see the structure of the table displayed like this: Dont be alarmed by the fact that Collation displays latin1_swedish_ci. MySQL was originally developed in Sweden, and Swedish uses the same sort order as English (and Finnish). The underlining of image_id indicates that its the tables primary key. To change any settings, click the pencil-like icon in the appropriate row. This opens a version of the previous screen and allows you to change the values. If you made a complete mess and want to start again, click the Drop tab at the top right of the screen, and confirm that you want to drop the table. (In SQL, delete refers only to records. You drop a table or a database.) Inserting records into a table Now that you have a table, you need to put some data into it. Eventually, youll need to build your own content management system using HTML forms, PHP, and SQL; but the quick and easy way to do it is with phpMyAdmin. Using phpMyAdmin to insert records manually These instructions show how to add individual records to the images table through the phpMyAdmin interface. 1. If phpMyAdmin is still displaying the structure of the images table as at the end of the previous section, skip to step 2. Otherwise, launch phpMyAdmin, and select the phpsols database from the drop-down menu in the left frame. Then click the Structure icon alongside images, as shown in the following screenshot: CHAPTER 10 294 The breadcrumb trail at the top of the main frame provides the context for the tabs across the head of the page. The Structure tab at the top left of the preceding screenshot refers to the structure of the phpsols database. At the moment, it contains only one table, images . To access the structure of an individual table, click the Structure icon alongside its name. Use your mouse pointer to reveal tooltips for each icon. Some, such as Browse , are grayed out because there are no records in the table. 2. Click the Inser t tab in the center top of the page. This displays the following screen, ready for you to insert up to two records: 3. The forms display the names and details of each column. You can ignore the Function fields. MySQL has a large number of functions that you can apply to the values being stored in your GETTING STARTED WITH MYSQL 295 table. Youll learn more about them in the following chapters. The Value field is where you enter the data you want to insert in the table. Because you have defined image_id as AUTO_INCREMENT, MySQL inserts the next available number automatically. So you must leave the image_id Value field blank. Fill in the next two Value fields as follows: • filename: basin.jpg • caption: Water basin at Ryoanji temple, Kyoto 4. In the second form, leave the Value field for image_id blank, and fill in the next two fields like this: • filename: fountains.jpg • caption: Fountains in central Tokyo Normally, the Ignore check box is automatically deselected when you add values to the second form, but deselect it if necessary. 5. Click Go. The SQL used to insert the records is displayed at the top of the page, together with a report that two rows have been inserted. Ill explain the basic SQL commands in the remaining chapters, but studying the SQL that phpMyAdmin displays is a good way to learn how to build your own queries. SQL is closely based on human language, so it isnt all that difficult to learn. 6. Click the Brows e tab at the top left of the page. You should now see the first two entries in the images table, as shown here: As you can see, MySQL has automatically inserted 1 and 2 in the image_id fields. You could continue typing out the details of the remaining six images, but lets speed things up a bit by using a SQL file that contains all the necessary data. Loading the images records from a SQL file Because the primary key of the images table has been set to AUTO_INCREMENT, its necessary to drop the original table and all its data. The SQL file does this automatically and builds the table from scratch. These instructions assume that phpMyAdmin is open at the page in step 6 of the previous section. 1. If youre happy to overwrite the data in the images table, skip to step 2. However, if you have entered data that you dont want to lose, copy your data to a different table. Click the Operations tab at the top of the page, type the name of the new table in the blank field in the section titled Copy table to (database.table), and click Go. The following screenshot shows the settings for copying the images table to images_backup: CHAPTER 10 296 2. After clicking Go, you should see confirmation that the table has been copied. The breadcrumb trail at the top of the page indicates that phpMyAdmin is still in the images table, so you can proceed to step 2, even though you have a different page onscreen. 3. Click the Import tab at the top right of the page. In the next screen, click the Browse (or Choose File) button in File to import, and navigate to images.sql in the ch10 folder. Leave all options at their default setting, and click Go at the foot of the page. 4. phpMyAdmin drops the original table, creates a new version, and inserts all the records. When you see confirmation that the file has been imported, click the Brows e button at the top left of the page. You should now see the same data as shown in Figure 10-1 at the beginning of the chapter. If you open the images.sql in a text editor, youll see that it contains the SQL commands that create the images table and populate it with data. This is how the table is built: DROP TABLE IF EXISTS `images`; CREATE TABLE IF NOT EXISTS `images` ( `image_id` int(10) unsigned NOT NULL AUTO_INCREMENT, `filename` varchar(25) NOT NULL, `caption` varchar(120) NOT NULL, PRIMARY KEY (`image_id`) ) ENGINE=MyISAM DEFAULT CHARSET=latin1 AUTO_INCREMENT=9 ; GETTING STARTED WITH MYSQL 297 Importing data from a SQL file like this is how you transfer data from your local testing environment to the remote server where your website is located. Assuming that your hosting company provides phpMyAdmin to administer your remote database, all you need to do to transfer the data is to launch the version of phpMyAdmin on your remote server, click the Import tab, select the SQL file on your local computer, and click Go. The next section describes how to create the SQL file. Creating a SQL file for backup and data transfer MySQL doesnt store your database in a single file that you can simply upload to your website. Even if you find the right files (on Windows, theyre located in C:\Program Files\MySQL\MySQL Server 5.1\data), youre likely to damage them unless the MySQL server is turned off. Anyway, most hosting companies wont permit you to upload the raw files because it would also involve shutting down their server, causing a great deal of inconvenience for everyone. Nevertheless, moving a database from one server to another is very easy. All it involves is creating a backup dump of the data and loading it into the other database with phpMyAdmin or any other database administration program. The dump is a text file that contains all the necessary SQL commands to populate an individual table or even an entire database elsewhere. phpMyAdmin can create backups of your entire MySQL server, individual databases, selected tables, or individual tables. To keep things simple, these instructions show you how to back up only a single database. 1. In phpMyAdmin, select the phpsols database from the drop-down menu in the navigation frame. If the database was already selected, click the Database: phpsols breadcrumb at the top of the screen, as shown here: 2. Select Export from the tabs along the top of the screen. 3. The rather fearsome looking screen shown in Figure 10-6 opens. In spite of all the options, you need to concern yourself with only a few. • The Export section on the left of the screen lists all the tables in your database. Click Select All, and leave the radio buttons on the default SQL. • If the database has ne ver been transferred to the other server before, the only option that you need to set on the right side of the screen is the drop-down menu labeled SQL export compatibility. If the other server is running MySQL 3.23, choose MYSQL323. If the other server is running MySQL 4.0, choose MYSQL40. Otherwise, choose NONE. • If the database has already been transferred on a previous occasion, select Add DROP TABLE in the Structure section. The existing contents of each table are dropped and are replaced with the data in the backup file. CHAPTER 10 298 Figure 10-6. phpMyAdmin offers a wide range of choices when exporting data from MySQL. 4. Make sure the check box labeled Save as file at the bottom of the screen is selected. The default setting in File name template is __DB__, which automatically gives the backup file the same name as your database. So, in this case, it becomes phpsols.sql. If you add anything after the final double underscore, phpMyAdmin adds this to the name. For instance, GETTING STARTED WITH MYSQL 299 you might want to indicate the date of the backup, so you could add 2011-11-11 for a backup made on November 11, 2011. The file would then be named phpsols2011-11-11.sql. 5. If your database contains a lot of data, select a compression format from one of the radio buttons at the bottom of the page. When you import the file to another server, phpMyAdmin automatically decompresses it. 6. Click Go, and save the SQL file to your local hard disk. You now have a backup that can be used to transfer the contents of your database to another server. The file created by phpMyAdmin contains the SQL commands only to create and populate the database tables. It does not include the command to create the database. This means you can import the tables into any database. It does not need to have the same name as the one in your local testing environment. Choosing the right data type in MySQL You may have received a bit of a shock when selecting Type for the image_id column. phpMyAdmin lis ts all available data types—there are nearly 40 in MySQL 5.1. Rather than confuse you with unnecessary details, Ill explain just the most commonly used. You can find full details of all data types in the MySQL documentation at http://dev.mysql.com/ doc/refman/5.1/en/data-types.html. Storing text The difference between the main text data types boils down to the maximum number of characters that can be stored in an individual field, the treatment of trailing spaces, and whether you can set a default value. • CHAR: A fixed-length string. You must specify the required length in the Length/Values field. The maximum permitted value is 255. Internally, strings are right-padded with spaces to the specified length, but the trailing spaces are stripped when you retrieve the value. You can define a default. • VARCHAR: A variable-length string. You must specify the maximum number of characters you plan to use (in phpMyAdmin, enter the number in the Length/Values field). Prior to MySQL 5.0, the limit was 255. This was increased to 65,535 in MySQL 5.0. If a string is stored with trailing spaces, they are preserved on retrieval. Accepts a default value. • TEXT: Stores text up to a maximum of 65,535 characters (approximately 50% longer than this chapter). Cannot define a default value. TEXT is convenient because you dont need to specify a maximum size (in fact, you cant). Although the maximum length of VARCHAR is the same as TEXT in MySQL 5.0 and later, other factors may limit the actual amount that can be stored. Keep it simple: use VARCHAR for short text items and TEXT for longer ones. CHAPTER 10 300 Storing numbers The most frequently used numeric column types are as follows: • INT: Any whole number (integer) between –2,147,483,648 and 2,147,483,647. If the column is declared as UNSIGNED, the range is from 0 to 4,294,967,295. • FLOAT: A floating-point number. You can optionally specify two comma-separated numbers to limit the range. The first number specifies the maximum number of digits, and the second specifies how many of those digits should come after the decimal point. Since PHP will format numbers after calculation, I recommend that you use FLOAT without the optional parameters. • DECIMAL: A number with a fraction containing a fixed number of digits after the decimal point. When defining the table, you need to specify the maximum number of digits and how many of those digits should come after the decimal point. In phpMyAdmin, enter the numbers separated by a comma in the Length/Values field. For example, 6,2 permits numbers in the range from –9999.99 to 9999.99. If you dont specify the size, the decimal fraction is truncated when values are stored in this type of column. The difference between FLOAT and DECIMAL is accuracy. Floating-point numbers are treated as approximate values and are subject to rounding errors (for a detailed explanation, see http://dev.mysql.com/doc/refman/5.1/en/problems-with-float.html). Use DECIMAL to store currencies. However, its important to note that prior to MySQL 5.0.3, the DECIMAL data type was stored as a string, so could not be used with SQL functions, such as SUM(), to perform calculations inside the database. If your remote server is running an older version of MySQL, store currencies in an INT column as cents; for pounds, use pence. Then use PHP to divide the result by 100, and format the currency as desired. Better still, move to a server that runs MySQL 5.0 or higher. Dont use commas or spaces as the thousands-separator. Apart from numerals, the only characters permitted in numbers are the negative operator (-) and the decimal point (.). Storing dates and times MySQL stores dates in one format only: YYYY-MM-DD. Its the standard approved by the ISO (International Organization for Standardization) and avoids the ambiguity inherent in different national conventions. Ill return to the subject of dates in Chapter 14. The most important column types for dates and times are as follows: • DATE: A date stored as YYYY-MM-DD. The range is 1000-01-01 to 9999-12-31. • DATETIME: A combined date and time displayed in the format YYYY-MM-DD HH:MM:SS. • TIMESTAMP: A timestamp (normally generated automatically by the computer). Legal values range from the beginning of 1970 to partway through January 2038. . through the phpMyAdmin interface. 1. If phpMyAdmin is still displaying the structure of the images table as at the end of the previous section, skip to step 2. Otherwise, launch phpMyAdmin,. you prefer to use Navicat, SQLyog, or a different UI for MySQL, use the settings in Table 1 0-1 . 1. Launch phpMyAdmin, if its not already open, and select phpsols from the Database drop- down. individual tables. To keep things simple, these instructions show you how to back up only a single database. 1. In phpMyAdmin, select the phpsols database from the drop-down menu in the navigation