The process of php accessing the database

When making a dynamic website, the most basic step is to connect to the database. Below we will introduce the process of connecting to the database in PHP.

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1. Connect database function

mysqli_connect(hostname, username, password) The return value is one of our connection objects. If the connection fails, an error will be returned and false

2. Judgment error function

mysqli_connect_error (connection object) Error message Return error message

mysqli_connect_errno (connection object) Error number 0 means the connection is successful and there is no error

3. Select database function

mysqli_select_db (connection object, database name to be selected); If the selection is successful, return true, otherwise return false

4. Select character set

mysqli_set_charset (connection object, character set to be selected); if the selection is successful, return true, otherwise return false

5. Prepare sql statement

6. Send sql statement

Mysqli_query (connection object, required Sq l statement sent); Successfully obtains an object. Failure returns false

7. Processing the result set

7.1 Get the number of entries

a) mysqli_num_rows (the object that successfully sent the sql) is used to obtain the number of records obtained by the query. It can only be used in select statements

b) mysqli_affected_rows (the connection object) the previous mysql operation Number of rows affected Only INSERT UPDATE DELETE operation uses return value 1 Number of successfully inserted rows -1 Execution failed

7.2 Get the contents of the query result set

mysqli_fetch_array( Send object) Return the results of the query in the form of a mixed array and return one item at a time

Mysqli_fetch_row (Send object) Return the results of the query in the form of an index array Return one item at a time

mysqli_fetch_assoc( Send object) Return the results of the query in the form of an associative array. Return one item at a time

7.3 When adding the operation, we can get the last inserted id

mysqli_insert_id (Connection object) Returns the last inserted id

8. Close the database

Mysqli_close (Connection object)

// 1.连接数据库
// 2.判断错误
// 3.选择数据库
// 4.选择字符集
// 5.准备sql语句
// 6.发送sql语句
// 7.处理结果集
// 8.关闭数据库

//1.连接数据库
//mysqli_connect('主机名','用户名','密码');
$link=@mysqli_connect('localhost','root','123456');
//var_dump($link);

//2.判断错误
//mysqli_connect_error(连接对象) 错误信息
//mysqli_connect_errno(连接对象)   错误号
// echo mysqli_connect_errno($link);
// echo mysqli_connect_error($link);
if(mysqli_connect_errno($link)){
echo mysqli_connect_error($link);exit;
//echo '错误了 重新连接';exit;
}

//3.选择数据库
mysqli_select_db($link,'ss21');

//4.选择字符集
mysqli_set_charset($link,'utf8');

//5.准备sql语句
$sql="SELECT id,name,sex,age,city FROM info";
//$sql="INSERT INTO info(name) VALUES(NULL)";

//6.发送sql语句
$result = mysqli_query($link,$sql);

//7.处理结果集
echo mysqli_num_rows($result);
//echo mysqli_affected_rows($link);

//8.关闭数据库
mysqli_close($link);

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