使用 PHP 检查 SQL 行是否存在

发布于 2024-11-19 04:22:53 字数 134 浏览 1 评论 0原文

我将 MySQL 与 PHP 结合使用，我需要做这样的事情（伪代码）：

if (sql row exists where username='bob')
{
    // do this stuff
}

原文

I'm using MySQL with PHP and I need to do something like this (pseudocode):

if (sql row exists where username='bob')
{
    // do this stuff
}

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东走西顾 2024-11-26 04:22:53

如果您想使用 PDO（PHP 数据对象），然后使用以下代码：

$dbh = new PDO("mysql:host=your_host_name;dbname=your_db_name", $user, $pass);
$stmt = $dbh->prepare("SELECT username from my_table where username = ':name'");
$stmt->bindParam(":name", "bob");
$stmt->execute();

if($stmt->rowCount() > 0)
{
    // row exists. do whatever you want to do.
}

If you would like to use PDO (PHP Data Object), then use the following code:

$dbh = new PDO("mysql:host=your_host_name;dbname=your_db_name", $user, $pass);
$stmt = $dbh->prepare("SELECT username from my_table where username = ':name'");
$stmt->bindParam(":name", "bob");
$stmt->execute();

if($stmt->rowCount() > 0)
{
    // row exists. do whatever you want to do.
}

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原谅过去的我 2024-11-26 04:22:53

Sayem 的答案得到了最多的支持，但我认为它对于 PDO 来说是不正确的。

来自 PHP 文档：

对于大多数数据库， PDOStatement::rowCount( ) 不返回受 SELECT 语句影响的行数。相反，使用 PDO::query() 发出 SELECT COUNT(*) 语句，其谓词与预期的 SELECT 语句相同，然后使用 PDOStatement::fetchColumn() 检索将返回的行数。

$sql = "SELECT COUNT(*) FROM fruit WHERE calories > 100";
$res = $conn->query($sql);

/* Check the number of rows that match the SELECT statement */
if ($res->fetchColumn() > 0) {
    /* Issue the real SELECT statement and work with the results */
    $sql = "SELECT name FROM fruit WHERE calories > 100";
    foreach ($conn->query($sql) as $row) {
        print "Name: " .  $row['NAME'] . "\n";
    }
}
/* No rows matched -- do something else */
else {
    print "No rows matched the query.";
}

Sayem's answer has the most upvotes, but I believe it is incorrect regarding PDO.

From the PHP docs:

For most databases, PDOStatement::rowCount() does not return the number of rows affected by a SELECT statement. Instead, use PDO::query() to issue a SELECT COUNT(*) statement with the same predicates as your intended SELECT statement, then use PDOStatement::fetchColumn() to retrieve the number of rows that will be returned.

$sql = "SELECT COUNT(*) FROM fruit WHERE calories > 100";
$res = $conn->query($sql);

/* Check the number of rows that match the SELECT statement */
if ($res->fetchColumn() > 0) {
    /* Issue the real SELECT statement and work with the results */
    $sql = "SELECT name FROM fruit WHERE calories > 100";
    foreach ($conn->query($sql) as $row) {
        print "Name: " .  $row['NAME'] . "\n";
    }
}
/* No rows matched -- do something else */
else {
    print "No rows matched the query.";
}

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不顾 2024-11-26 04:22:53

另一种方法

$user = "bob";
$user = mysql_real_escape_string($user);
$result = mysql_query("SELECT COUNT(*) AS num_rows FROM my_table WHERE username='{$user}' LIMIT 1;");
$row = mysql_fetch_array($result);
if($row["num_rows"] > 0){
   //user exists
}

another approach

$user = "bob";
$user = mysql_real_escape_string($user);
$result = mysql_query("SELECT COUNT(*) AS num_rows FROM my_table WHERE username='{$user}' LIMIT 1;");
$row = mysql_fetch_array($result);
if($row["num_rows"] > 0){
   //user exists
}

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~没有更多了~