Database query operation in php

Database query operation in php

Recommended related mysql video tutorials: "mysql tutorial"

* 1. Query Operation

* 2. Three functions involved:

* 2-1. mysqli_query($db, $sql): Execute SQL statement and return the result set

* 2-2. mysqli_errno($db): Returns the error code of the last function execution

* 2-3. mysqli_error($db): Returns the error message of the last function execution

* 2-4. mysqli_num_rows($res): Returns the number of records in the result set

* 2-5. mysqli_fetch_row($res): Returns a record in an index array

* 2-5. mysqli_fetch_assoc($res): Returns a record as an associative array

* 2-5. mysqli_fetch_array($res,MYSQLI_NUM): Returns a record as an index array

* 2-5. mysqli_fetch_array( $res,MYSQLI_ASSOC): Returns a record as an associative array

* 2-5. mysqli_fetch_array($res,MYSQLI_BOTH): Returns a record as an index and relational array

* 2-5 . mysqli_fetch_object($res): Return a record in object mode

* mysqli_free_result($result);

* 2-4. mysqli_close($db): Close the current data connection

* 3. Query steps:

* 3-1. Connect to the database

* 3-2. Prepare SQL statements

* 3-3. Execute query

* 3-4. Detection result

* 3-5. If it is select, return the result set

* 3-5-1. If it is insert/update /delete: Returns the number of affected records

* 3-6. Close the database connection

//1. Connect to the database, require is not a function, no need to add brackets after it

define ('DB_HOST', 'localhost');
define ('DB_USER', 'root');
define ('DB_PASS', 'root');
define ('DB_NAME', 'php');
define ('DB_CHAR', 'utf8');
$db = @mysqli_connect(DB_HOST, DB_USER, DB_PASS);
if (mysqli_connect_errno($db)) {
    exit('连接失败'.mysqli_connect_error($db));
}
mysqli_select_db($db, DB_NAME);
mysqli_set_charset($db, DB_CHAR);

//2. Prepare SQL statement

$sql = "SELECT name,salary FROM staff";
$sql = "SELECT name AS 姓名,salary AS 工资 FROM staff WHERE age>90";

//3. Execute the query: the result set object will be returned if successful, false

$result = mysqli_query($db, $sql);
var_dump($result);die();

//4. Detection results

//If the result set exists

if (false != $result) { //这是写只是语义性更强
    //如果结果集中存在记录,至少有一条
//    if (mysqli_num_rows($result) > 0) {
    //mysqli_affected_rows($db)也可以完成同样的检测工作,注意参数是连接对象$db,不是结果集对象
    if (mysqli_affected_rows($db) > 0) {
//        echo &#39;共计:&#39;.mysqli_num_rows($result).&#39;条记录<br>&#39;;
        echo &#39;共计:&#39;.mysqli_affected_rows($db).&#39;条记录~~<br>&#39;;

//5. Process the result set

//5-1: Get the index part

while($row = mysqli_fetch_array($result, MYSQLI_NUM)){

//Get the index part Shortcut method

while($row = mysqli_fetch_row($result)){

//5-2: Get the associated part

while($row = mysqli_fetch_array($result, MYSQLI_ASSOC)){

//Shortcut method to get the associated part

while($row = mysqli_fetch_assoc($result)){

//5-3: Index association

while($row = mysqli_fetch_array($result, MYSQLI_BOTH)){

//5-4: The quick way to get the index association is not to pass in the second parameter, which is the default value

while($row = mysqli_fetch_array($result)){

//5-4: In the form of objects

        while($row = mysqli_fetch_object($result)){
//            var_export($row);//以字符串方式表示查询结查
            //如果是对象,可以用指向符来访问
            echo $row->name.'--'.$row->salary;
            echo &#39;<hr>&#39;;
            //以变量方式表示,表示的内容更加完整丰富
//            var_dump($row);
        }
    } else {
        echo &#39;没有符合条件的记录&#39;;
    }
    //查询失败的处理方式
} else {
    //必须要用exit()或die()终止脚本执行,否则后面的语句还会执行并会报错
    exit(&#39;查询失败&#39;.mysqli_errno($db).&#39;:&#39;.mysqli_error($db));
}

//5. Release the result set (only for select)

mysqli_free_result($result);

//6. Close the database connection

mysqli_close($db);