PHP工作原理:
(1). PHP的代码传递给PHP包, 请求PHP进行解析并编译.
(2). 服务器根据PHP代码的请求读取数据库.
(3). 服务器与PHP包共同根据数据库中的数据和其他运行变量, 将PHP代码解析成普通的HTML代码.
(4). 解析后的代码发送个浏览器, 浏览器对代码进行分析获取可视化内容.
(5). 用户通过浏览器浏览网站的内容.
(1). 建立连接: $connection = mysqli_connect(‘host‘, ‘username‘, ‘password‘, ‘databases_name‘, port......);
(2). 判断连接是否成功: mysqli_connect_error()-----连接成功返回0, 失败返回1
(3). 选择数据库: mysqli_select_db($connection, ‘another_database_name‘)
(4). 设置字符集: mysql_set_charset($connection, ‘utf8‘);
(5). 书写SQL语句: $sql = "select * from db_name"; $result = mysqli_query($connection, $sql);.........
(6). 执行SQL语句: mysqli_query();
(7). 解析结果集: mysqli_fetch_array($result, resulttype::MYSQLI_ASSOC);
其中: MYSQLI_ASSOC代表以关联数组编号, MYSQLI_NUM代表以索引数组编号
mysqli_fetch_assoc(), mysqli_fetch_all();
(8). 关闭连接: mysqli_close($connection);
例如:
<?php //建立连接 $connection = mysqli_connect(‘localhost‘, ‘root‘, ‘root‘, ‘test‘, 3306); // var_dump($connection); //判断连接是否成功 if( !mysqli_connect_error() ){ echo ‘连接成功!‘.‘</br>‘; }else{ die(mysqli_connect_error()); } //(更换)选择数据库 mysqli_select_db($connection, ‘mrsoft‘); //设置字符集 mysqli_set_charset($connection, ‘utf8‘); //操作数据库 $sql = "select * from `books`"; $result = mysqli_query($connection, $sql); var_dump($result); $array = mysqli_fetch_array($result, MYSQLI_ASSOC); var_dump($array); //关闭连接 mysqli_close($connection); //var_dump($connection); ?>
说明: 如果在多个网页中都要进行频繁的数据库访问, 则可以建立与数据库服务器的持续连接来提高效率.
持续连接的方法: mysqli_pconnect()代替mysqli_connect(), 系统自动返回已经建立好的持续连接的ID号.
<?php //连接数据库 $connect = mysqli_connect(‘localhost‘, ‘root‘, ‘root‘, ‘test‘, 3306); //测试连接是否成功 if( mysqli_connect_error() ){ die(‘连接失败, 原因: ‘. mysqli_connect_error()); } //连接成功 //选择数据库 mysqli_select_db($connect, ‘test‘); //设置字符集 mysqli_set_charset($connect, ‘utf8‘); //书写SQL语句 $sql_insert =‘INSERT INTO user1(username, age, sex, addr, married, salary) VALUES("周星星", 28, "男", "香港", 0, 9999999)‘; $sql_update = ‘UPDATE user1 SET username="张三丰" WHERE id=5‘; $sql_delete = ‘DELETE FROM user1 WHERE id=4‘; //执行SQL语句 $result_insert = mysqli_query($connect, $sql_insert); $result_update = mysqli_query($connect, $sql_update); $result_delete = mysqli_query($connect, $sql_delete); //解析SQL语句执行结果 if($result_insert){ echo ‘执行成功!‘ . mysqli_affected_rows($connect) . ‘条数据, 刚才插入的数据的ID是‘ . mysqli_insert_id($connect); }else{ echo ‘执行失败!‘; } if($result_update){ echo ‘执行成功!‘ .‘更新了‘ .mysqli_affected_rows($connect) . ‘条数据.‘; }else{ echo ‘执行失败!‘; } if($result_delete){ echo ‘执行成功! 成功删除了‘.mysqli_affected_rows($connect) . ‘条数据.‘; }else{ echo ‘执行失败!‘; } //关闭连接, 释放资源. mysqli_close($connect); ?>
<?php //连接数据库 $link = mysqli_connect(‘localhost‘, ‘root‘, ‘root‘); //测试连接是否成功 if( mysqli_connect_error()){ die( ‘连接失败! 原因: ‘. mysqli_connect_error()); } //连接成功 //选择数据库test mysqli_select_db($link, ‘test‘); //设置字符集 mysqli_set_charset($link, ‘utf8‘); //书写SQL语句 $sql1 = ‘SELECT * FROM user1‘; $sql2 = ‘SELECT * FROM user1 WHERE id<8‘; //执行SQL语句 $result = mysqli_query($link, $sql2); //解析结果 if($result){ // echo ‘执行成功! ‘; echo ‘<pre>‘; // $data = mysqli_fetch_array($result, MYSQLI_ASSOC); // var_dump($data); while($row = mysqli_fetch_array($result, MYSQLI_ASSOC)){ var_dump($row); } }else{ echo ‘执行失败! ‘; } ?>
结果:
array(8) {
["id"]=>
string(1) "5"
["username"]=>
string(9) "张三丰"
["age"]=>
string(2) "38"
["sex"]=>
string(3) "男"
["addr"]=>
string(6) "上海"
["married"]=>
string(1) "0"
["salary"]=>
string(8) "15000.00"
["userDesc"]=>
string(16) "user description"
}
array(8) {
["id"]=>
string(1) "6"
["username"]=>
string(9) "张子怡"
["age"]=>
string(2) "39"
["sex"]=>
string(3) "女"
["addr"]=>
string(6) "北京"
["married"]=>
string(1) "1"
["salary"]=>
string(8) "85000.00"
["userDesc"]=>
string(16) "user description"
}
array(8) {
["id"]=>
string(1) "7"
["username"]=>
string(6) "汪峰"
["age"]=>
string(2) "42"
["sex"]=>
string(3) "男"
["addr"]=>
string(6) "深圳"
["married"]=>
string(1) "1"
["salary"]=>
string(8) "95000.00"
["userDesc"]=>
string(16) "user description"
}
<?php //连接数据库 $link = mysqli_connect(‘localhost‘, ‘root‘, ‘root‘); //测试连接是否成功 if( mysqli_connect_error() ){ die( ‘连接失败! 原因: ‘.mysqli_connect_error()); } //连接成功 //选择数据库 mysqli_select_db($link, ‘test‘); //设置字符集 mysqli_set_charset($link, ‘utf8‘); //书写SQL语句 $sql = ‘SELECT * FROM user1 WHERE id<12 AND id>8‘; //执行SQL语句 $result = mysqli_query($link, $sql); //解析SQL语句执行结果 if($result) { echo ‘<pre>‘; echo ‘<table border="1px">‘; echo ‘<tr>‘; echo ‘<th>id</th>‘; echo ‘<th>username</th>‘; echo ‘<th>age</th>‘; echo ‘<th>sex</th>‘; echo ‘<th>addr</th>‘; echo ‘<th>married</th>‘; echo ‘<th>salary</th>‘; echo ‘<th>userdesc</th>‘; echo ‘</tr>‘; while ($row = mysqli_fetch_array($result, MYSQLI_ASSOC)){ echo ‘<tr>‘; echo "<td width=‘100px‘>{$row[‘id‘]}</td>"; echo "<td width=‘100px‘>{$row[‘username‘]}</td>"; echo "<td width=‘100px‘>{$row[‘age‘]}</td>"; echo "<td width=‘100px‘>{$row[‘sex‘]}</td>"; echo "<td width=‘100px‘>{$row[‘addr‘]}</td>"; echo "<td width=‘100px‘>{$row[‘married‘]}</td>"; echo "<td width=‘100px‘>{$row[‘salary‘]}</td>"; echo "<td width=‘100px‘>{$row[‘userDesc‘]}</td>"; echo ‘</tr>‘; } echo ‘</table>‘; } //关闭连接 mysqli_close($link); ?>
结果:
(1)可能的错误原因:
SQL语句语法错误, 数据类型错误, 唯一索引列数据错误......
(2)程序错误排查:
判断SQL语句的执行结果, 查看数据影响条数, 获取SQL语句执行的错误信息[ 调用mysqli_error($link), mysqli_errorno($link) ]
原文：https://www.cnblogs.com/iceliu/p/11630080.html