PHP | MySQL WHERE 子句
WHERE子句用于仅过滤由用户给出的特定条件满足的那些记录。换句话说，SQL WHERE 子句用于限制受 SELECT、UPDATE 或 DELETE 查询影响的行数。
句法 ：
where 子句的基本语法是——
选择 Column1 ， Column2 ，...。
FROM 表名
WHERE 条件
WHERE 子句的实现：
让我们考虑下表“数据”，其中包含“名字”、“姓氏”和“年龄”三列。
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 子句：
0){
echo "";
echo "";
echo "Firstname ";
echo "Lastname ";
echo "age ";
echo " ";
while($row = mysqli_fetch_array($res)){
echo "";
echo "" . $row['Firstname'] . " ";
echo "" . $row['Lastname'] . " ";
echo "" . $row['Age'] . " ";
echo " ";
}
echo "
";
mysqli_free_result($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 ： 
代码说明：
- “res”变量存储函数mysql_query()返回的数据。
- 每次调用mysqli_fetch_array()时，它都会返回res()集中的下一行。
- while 循环用于循环遍历表“数据”的所有行。
使用面向对象方法的 Where 子句：
connect_error);
}
$sql = "SELECT * FROM Data WHERE Firstname='ram'";
if($res = $mysqli->query($sql)){
if($res->num_rows > 0){
echo "";
echo "";
echo "Firstname ";
echo "Lastname ";
echo "Age ";
echo " ";
while($row = $res->fetch_array()){
echo "";
echo "" . $row['Firstname'] . " ";
echo "" . $row['Lastname'] . " ";
echo "" . $row['Age'] . " ";
echo " ";
}
echo "
";
$res->free();
} else{
echo "No matching records are found.";
}
} else{
echo "ERROR: Could not able to execute $sql. "
. $mysqli->error;
}
$mysqli->close();
?>
输出 ： 
使用 PDO 方法的 Where 子句：
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($res->rowCount() > 0){
echo "";
echo "";
echo "Firstname ";
echo "Lastname ";
echo "Age ";
echo " ";
while($row = $res->fetch()){
echo "";
echo "" . $row['Firstname'] . " ";
echo "" . $row['Lastname'] . " ";
echo "" . $row['Age'] . " ";
echo " ";
}
echo "
";
unset($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 ： 