Introduction to basic steps for querying PHP Web databases

PHP is the preferred programming method for developing WEB dynamic pages. I have learned a lot from a book recently. Now I want to share with you the knowledge of PHP Web database query. Let's take a look at it. Basic Steps for querying a database from a PHP Web:

1. check and filter data from the user. First, we will filter the blank characters that the user may accidentally enter at the start or end of the search condition, which is implemented using the trim () function. The reason why we are so troublesome to check user input data is to prevent multiple interfaces from connecting to the database, because the user enters from different interfaces, which may cause security problems.

Then, when preparing to use any data entered by the user, filter some control characters as well. When the user inputs data to the database, the data must be escaped ,, in this case, the stolen functions include the addslashes () function, the stripslashes () function, and the get_magic_qutoes_gpc () function. The addslashes () function requires a backslash before certain characters for database query statements. The stripslashes () function removes the backslash character from the string. get_magic_qutoes_gpc () function magic adds the Escape Character "" to get the magic_quotes_runtime setting of the current activity configuration. If the magic quotation marks are disabled during runtime, 0 is returned; otherwise, 1 is returned. We can also use htmispecialchars () to encode special characters in HTML. The htmispecialchars () function converts some predefined characters into the predefined characters of HTML objects: & (and number) becomes & "(double quotation marks) becomes" '(single quotation marks) becomes' <(less than) becomes <> (greater than) become>

2. Establish a connection to the appropriate database. PHP provides the function library mysqli (I indicates improvement) for connecting to MySQL ).

When using the mysqli function library in PHP, you can use object-oriented or process-oriented Syntax:

1) object-oriented, @ $ db = new mysqli ('hostname', 'username', 'Password', 'dbname'); returns an object

2) process-oriented: @ $ db = mysqli_connect ('hostname', 'username', 'Password', 'dbname'); returns a resource, which indicates the database connection, if you use the procedure method, you must pass this resource to all other functions of mysqli.

This is very similar to processing functions. Most functions of mysqli have object-oriented interfaces and process interfaces. The difference between them is that the function name of the Process version starts with mysqli _, and mysqli_connect () is required () the resource handle obtained by the function. For this rule, data connection is an exception because it is created by the constructor of the mysqli object. Therefore, you must check the connection attempt. The mysqli_connect_errno () function returns an error code when a connection error occurs. If the connection is successful, 0 is returned.

Note: When connecting to the database, the common meeting error blocker @ is used as the first containing code. In this way, you can skillfully handle any errors or exceptions. In addition, MySQK limits the number of connections to the database at the same time. The MySQLi parameter max_connections determines the number of simultaneous connections. This parameter and the related Apache parameter MaxClients are used to tell the server to reject new connection requests, this ensures that system resources are no longer requested or used when the system is busy or when the system is paralyzed. To set the MaxClients parameter in Apache, edit the httpd. conf file in the system. To set the max_connections parameter for MySQLi, You can edit the file my. conf.

Select the database to use: use the use dbname command on the MySQL command line; use $ db-> select_db (dbname); or mysqli_select_db (db_resource, dbname) in php ).

3. to query a database, you must first construct a query statement: $ query = "select from user"; then run $ result = $ db-> query ($ query ); or $ result = mysqli_query ($ db, $ query). The object-oriented version returns a result object, and the procedural version returns a result resource. No matter which method saves the result in the $ result variable, it will be used after work. If the function fails to run, false is returned.

4. Obtain the query result using different functions to retrieve the query result from the result object or identifier in different ways. The result object or identifier is the key to accessing the returned row of the query.

We usually need to obtain the number of rows in the result set, and use the mysqli_fetch_assoc () function. Number of returned rows: $ num_results = $ result-> num_rows; (the number of rows is stored in the num_rows member variable of the object) or $ num_results = mysqli_num_rows ($ result). Then, each row is traversed cyclically, call $ row = $ result-> fectch_assoc () in a loop; or $ row = mysqli_fetch_assoc ($ result); to return information about the row. If the row is returned by an object, each keyword is an attribute name, and each value is the corresponding value in the attribute. If the row is returned by a resource, an array is returned.

There are other methods to get results from the result identifier, such as using $ row = $ result-> fecth_row ($ result); or $ row = mysqli_fetch_row ($ result ); return the result to an array. You can also use $ row = $ result-> fecth_object (); or $ row = mysqli_fecth_object ($ result ); jiang and his entourage go back to an object.

5. first release the result set from database disconnection: $ result-> free (); or mysqli_free_result ($ result); then close the database connection: $ db-> close () or mysqli_close ($ db); strictly speaking, this is not required because they will be automatically disabled when the script is executed.

The above are the basic steps for PHP Web database query. Do you know what you have learned? Try it now.