How to modify data in MySQL database using PHP

Assume you have successfully installed Apache, PHP and MySQL. If you haven't installed these applications yet, please install them first.

First, we need to log in to the MySQL database. Use the mysqli_connect function to establish a connection with the database. The following code demonstrates how to connect to a MySQL database:

<?php
   define(&#39;DB_SERVER&#39;, &#39;localhost&#39;);
   define(&#39;DB_USERNAME&#39;, &#39;username&#39;);
   define(&#39;DB_PASSWORD&#39;, &#39;password&#39;);
   define(&#39;DB_DATABASE&#39;, &#39;database_name&#39;);
   $db = mysqli_connect(DB_SERVER,DB_USERNAME,DB_PASSWORD,DB_DATABASE);
?>

In this example, we define the constants DB_SERVER, DB_USERNAME, DB_PASSWORD and DB_DATABASE, and then use the mysqli_connect function to connect to the MySQL database. If the connection is successful, we will get a $db handle that can be used to execute SQL queries.

Now, we can use PHP to execute SQL queries and update data. The following example illustrates how to use PHP to modify data in a MySQL database:

<?php
   // 连接到数据库
   $db = mysqli_connect(&#39;localhost&#39;,&#39;username&#39;,&#39;password&#39;,&#39;database_name&#39;);
   
   // 更新数据
   $query = "UPDATE table_name SET column1=value1,column2=value2,... WHERE some_column=some_value";
   $result = mysqli_query($db, $query);
   if ($result) {
       echo "数据更新成功";
   } else {
       echo mysqli_error($db);
   }
?>

In this example, we use the SQL statement UPDATE to update the data. The format of this statement is:

UPDATE table_name SET column1=value1,column2=value2,... WHERE some_column=some_value

where table_name is the table name, column1=value1, column2=value2 are the columns to be updated name and value. The WHERE clause specifies the rows to be updated, which can filter data based on specific column values.

In our example, we will update the column1 and column2 columns in the table_name table, setting their values ​​to value1 and value2. The WHERE clause will filter data based on the some_column=some_value condition.

Finally, we use the mysqli_query function to execute the query and output messages based on the query results.

In addition to the UPDATE statement, there are other types of SQL query statements that can be used to modify data in the MySQL database. For example, we can add new data to the table using the INSERT INTO statement:

INSERT INTO table_name (column1,column2,column3,...) VALUES (value1,value2,value3,...)

We can also delete data from the table using the DELETE statement:

DELETE FROM table_name WHERE some_column=some_value

Finally, we need to note that you should be extra careful when using PHP to modify the MySQL database, especially when modifying user input data. To prevent attacks such as SQL injection, input data must be properly validated and filtered.

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