postgresql检查执行预准备语句时是否存在

Question

我在准备一些语句，并希望在更新之前检查该行是否存在。如果存在，则更新它，如果它不存在，则输出消息“没有这种动物”。我有更新位工作，但不确定如何检查行是否存在。请协助。

$v = array(); 
$v[] = $_POST['status']; 
$v[] = $_POST['id']; 

$dbh = dbh_get(); 

$sql = 'UPDATE tap SET status=? 
    WHERE id =?'; 

$stmt = $dbh->prepare($sql); 
$stmt->execute($v); 

\\ if row isn't there display message "No such animal" 

\\ otherwise print the below 

printf("Status was changed to - %s", $v[0]); 

\\then either way have my continue button for me to click on 

print '<div class="button" style="float:left;" onclick="window.location.href=\'admin.php\';">Admin</div>' . "\n"; 

dbh_free($dbh) 

Answer 1

根据你的问题，你想检查行是否存在之前执行更新。你可以试试这个 -

$id_exist = 0; 
$sql = "SELECT id 
     FROM tap" ; 

$sql_prepare = $dbh->prepare($sql); 
$sql_prepare->execute(); 
while($row = $sql_prepare->fetchObject()) { 
    if($_POST['id'] == $row->id) { 
     $id_exist = 1; 
    } 

} 
if($id_exist == 1) { 
// perform update here 
} else { 
    echo 'No such animal'; 
}