PHP | MySQL选择查询-yiteyi-C++库

SQL 选择语句用于从数据库表中选择记录。

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语法： select子句的基本语法是——

要从表中选择所有列，请 $*$ 使用字符。

Select查询的实现： 让我们考虑下表“数据”，有三列“FiestNeX”、“LaSTNED”和“AGE”。图片[4]-PHP | MySQL选择查询-yiteyi-C++库

要选择“数据”表中存储的所有数据，我们将使用下面提到的代码。

选择“使用过程方法查询”：

                       <?php                     
                       $link = mysqli_connect(                                  "localhost"                                  ,                                  "root"                                  ,                                  ""                                  ,                                  "Mydb"                                  );                     
                                
                       if                                  ($link == =                                  false                                  ) {                     
                                             die(                                  "ERROR: Could not connect. "                     
                                             .mysqli_connect_error());                     
                       }                     
                                
                       $sql =                                  "SELECT * FROM Data"                                  ;                     
                       if                                  ($res = mysqli_query($link, $sql)) {                     
                                             if                                  (mysqli_num_rows($res) > 0) {                     
                                             echo                                  "<table>"                                  ;                     
                                             echo                                  "<tr>"                                  ;                     
                                             echo                                  "<th>Firstname</th>"                                  ;                     
                                             echo                                  "<th>Lastname</th>"                                  ;                     
                                             echo                                  "<th>age</th>"                                  ;                     
                                             echo                                  "</tr>"                                  ;                     
                                             while                                  ($row = mysqli_fetch_array($res)) {                     
                                             echo                                  "<tr>"                                  ;                     
                                             echo                                  "<td>"                                  .$row[                                  'Firstname'                                  ].                                  "</td>"                                  ;                     
                                             echo                                  "<td>"                                  .$row[                                  'Lastname'                                  ].                                  "</td>"                                  ;                     
                                             echo                                  "<td>"                                  .$row[                                  'Age'                                  ].                                  "</td>"                                  ;                     
                                             echo                                  "</tr>"                                  ;                     
                                             }                     
                                             echo                                  "</table>"                                  ;                     
                                             mysqli_free_res($res);                     
                                             }                     
                                             else                                  {                     
                                             echo                                  "No matching records are found."                                  ;                     
                                             }                     
                       }                     
                       else                                  {                     
                                             echo                                  "ERROR: Could not able to execute $sql. "                     
                                             .mysqli_error($link);                     
                       }                     
                       mysqli_close($link);                     
                       ?>                     

输出： 图片[4]-PHP | MySQL选择查询-yiteyi-C++库

代码说明：

“res”变量存储函数返回的数据 mysql_query（） .
每次 mysqli_fetch_array（） 调用时，它将从 res（） 设置
while循环用于循环表“data”的所有行。

选择使用面向对象方法进行查询：

                       <?                                  php                     
                       $                                  mysqli                                  =                                  new                                  mysqli("localhost", "root", "", "Mydb");                     
                                
                       if ($mysqli == = false) {                     
                                             die("ERROR: Could not connect. "                     
                                             .$mysqli->connect_error);                     
                       }                     
                                
                       $sql = "SELECT * FROM Data";                     
                       if ($res = $mysqli->query($sql)) {                     
                                             if ($res->num_rows > 0) {                     
                                             echo "<                                  table                                  >";                     
                                             echo "<                                  tr                                  >";                     
                                             echo "<                                  th                                  >Firstname</                                  th                                  >";                     
                                             echo "<                                  th                                  >Lastname</                                  th                                  >";                     
                                             echo "<                                  th                                  >Age</                                  th                                  >";                     
                                             echo "</                                  tr                                  >";                     
                                             while ($row = $res->fetch_array())                     
                                             {                     
                                             echo "<                                  tr                                  >";                     
                                             echo "<                                  td                                  >".$row['Firstname']."</                                  td                                  >";                     
                                             echo "<                                  td                                  >".$row['Lastname']."</                                  td                                  >";                     
                                             echo "<                                  td                                  >".$row['Age']."</                                  td                                  >";                     
                                             echo "</                                  tr                                  >";                     
                                             }                     
                                             echo "</                                  table                                  >";                     
                                             $res->free();                     
                                             }                     
                                             else {                     
                                             echo "No matching records are found.";                     
                                             }                     
                       }                     
                       else {                     
                                             echo "ERROR: Could not able to execute $sql. "                     
                                             .$mysqli->error;                     
                       }                     
                       $mysqli->close();                     
                       ?>                     

输出： 图片[4]-PHP | MySQL选择查询-yiteyi-C++库

选择使用PDO方法查询：

                       <?                                  php                     
                       try {                     
                                             $                                  pdo                                  =                                  new                                  PDO("                                  mysql:host                                  =                                  localhost                                  ;                     
                                             dbname                                  =                                  mydb                                  ", "root", "");                     
                                             $pdo->setAttribute(PDO::ATTR_ERRMODE,                     
                                             PDO::ERRMODE_EXCEPTION);                     
                       }                     
                       catch (PDOException $e) {                     
                                             die("ERROR: Could not connect. ".$e->getMessage());                     
                       }                     
                       try {                     
                                             $sql = "SELECT * FROM Data";                     
                                             $res = $pdo->query($sql);                     
                                             if ($res->rowCount() > 0) {                     
                                             echo "<                                  table                                  >";                     
                                             echo "<                                  tr                                  >";                     
                                             echo "<                                  th                                  >Firstname</                                  th                                  >";                     
                                             echo "<                                  th                                  >Lastname</                                  th                                  >";                     
                                             echo "<                                  th                                  >Age</                                  th                                  >";                     
                                             echo "</                                  tr                                  >";                     
                                             while ($row = $res->fetch()) {                     
                                             echo "<                                  tr                                  >";                     
                                             echo "<                                  td                                  >".$row['Firstname']."</                                  td                                  >";                     
                                             echo "<                                  td                                  >".$row['Lastname']."</                                  td                                  >";                     
                                             echo "<                                  td                                  >".$row['Age']."</                                  td                                  >";                     
                                             echo "</                                  tr                                  >";                     
                                             }                     
                                             echo "</                                  table                                  >";                     
                                             unset($res);                     
                                             }                     
                                             else {                     
                                             echo "No matching records are found.";                     
                                             }                     
                       }                     
                       catch (PDOException $e) {                     
                                             die("ERROR: Could not able to execute $sql. "                     
                                             .$e->getMessage());                     
                       }                     
                       unset($pdo);                     
                       ?>                     

输出： 图片[4]-PHP | MySQL选择查询-yiteyi-C++库

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