PHP | MySQL WHERE子句-yiteyi-C++库

这个哪里子句仅用于筛选由用户给定的特定条件满足的记录。换句话说，SQLWHERE子句用于限制受SELECT、UPDATE或DELETE查询影响的行数。

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语法： where子句的基本语法是—— 选择第1列、第2列等…。来自表_Name 条件在哪里

WHERE条款的实施：

让我们考虑下表“数据”，有三列“FieldNeX”、“LaSTNED”和“AGE”。

图片[1]-PHP | MySQL WHERE子句-yiteyi-C++库

要选择“Firstname”为“ram”的所有行，我们将使用以下代码：

使用程序方法的Where条款：

                       <?                                  php                     
                       $                                  link                                  =                                  mysqli_connect                                  ("localhost", "root", "", "Mydb");                     
                                
                       if($link === false){                     
                                             die("ERROR: Could not connect. "                     
                                             . mysqli_connect_error());                     
                       }                     
                                
                       $                                  sql                                  =                                  "SELECT * FROM Data WHERE Firstname='ram'"                                  ;                     
                       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                                  >" . $row['Age'] . "</                                  td                                  >";                     
                                             echo "</                                  tr                                  >";                     
                                             }                     
                                             echo "</                                  table                                  >";                     
                                             mysqli_free_result($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[2]-PHP | MySQL WHERE子句-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。

Where子句使用面向对象方法：

                       <?                                  php                     
                       $                                  mysqli                                  =                                  new                                  mysqli("localhost", "root", "", "Mydb");                     
                                
                       if($mysqli === false){                     
                                             die("ERROR: Could not connect. "                     
                                             . $mysqli->connect_error);                     
                       }                     
                                
                       $sql = "SELECT * FROM Data WHERE Firstname='ram'";                     
                       if($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[3]-PHP | MySQL WHERE子句-yiteyi-C++库

使用PDO方法的Where子句：

                       <?                                  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 WHERE Firstname='ram'";                     
                                             $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 records matching are found.";                     
                                             }                     
                       } catch(PDOException $e){                     
                                             die("ERROR: Could not able to execute $sql. "                     
                                             . $e->getMessage());                     
                       }                     
                                
                       unset($pdo);                     
                       ?>                     

输出： 图片[3]-PHP | MySQL WHERE子句-yiteyi-C++库

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