How to use PHP to query database values ​​for operation

PHP is a very popular server-side programming language that is widely used for web development. In web development, PHP is often used with databases to better manage and manipulate data. In this article, we will introduce how to use PHP to query database values ​​for operation.

First, we need to connect to the database. PHP provides many libraries and extensions to connect to different types of databases, such as MySQL, Oracle, SQL Server, etc. In this article, we will use MySQL as an example to demonstrate.

To connect to a MySQL database, we can use PHP's built-in mysql_connect function, which accepts four parameters: host name, user name, password, and database name. Here is an example:

//连接到MySQL数据库
$con = mysql_connect("localhost","username","password");
if (!$con){
    die('Could not connect: ' . mysql_error());
}
//选择数据库
mysql_select_db("database_name", $con);

Once connected to the database, we can start querying the data. In PHP, the most commonly used function to query data is the mysql_query function. This function accepts a SQL query string as a parameter and returns a result set object that we can use to process the query results. Here is an example:

//查询数据库
$result = mysql_query("SELECT * FROM table_name");
if (!$result) {
    die('Invalid query: ' . mysql_error());
}
//遍历结果集
while($row = mysql_fetch_array($result)){
    echo $row['column_name'];
}

In the above example, we query all columns and rows in a table named "table_name" and iterate through each row in the result set. For each row, we output the value of the column named "column_name".

In addition to the SELECT statement, we can also use other types of SQL statements to operate the database. For example, we can insert a new row into the database using the INSERT statement:

//插入新行到数据库
mysql_query("INSERT INTO table_name (column1, column2, column3)
VALUES ('value1', 'value2', 'value3')");

In the above example, we inserted a new row into the "table_name" table, which contains three columns: column1, column2, and column3. Each column has a value, "value1", "value2", and "value3".

We can also use the UPDATE statement to update the value of the data row:

//更新数据库中的数据
mysql_query("UPDATE table_name SET column1='new_value'
WHERE column2='value2'");

In the above example, we use the UPDATE statement to update the column with the value "value2" in the table "table_name" The value of column "column1" in the row of "column2" is updated to "new_value".

Finally, we can use the DELETE statement to delete data rows in the database:

//从数据库中删除行
mysql_query("DELETE FROM table_name WHERE column1='value1'");

In the above example, we use the DELETE statement to delete all tables in the table "table_name" that contain the value " value1" row.

In short, PHP provides many functions and statements to operate the database. By mastering these technologies, we can manage and manipulate data more effectively, making our web applications more powerful and flexible.

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