使用 PHP 检查 SQL 行是否存在
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check if SQL row exists with PHP
提问by John
I'm using MySQL with PHP and I need to do something like this (pseudocode):
我在 PHP 中使用 MySQL，我需要做这样的事情（伪代码）：
if (sql row exists where username='bob')
{
// do this stuff
}
回答by MD Sayem Ahmed
If you are using mysql database, then use the following -
如果您使用的是 mysql 数据库，请使用以下命令 -
$query = "SELECT username from my_table where username='bob'";
$result = mysql_query($query);
if(mysql_num_rows($result) > 0)
{
// row exists. do whatever you would like to do.
}
If you would like to use PDO (PHP Data Object), as alex suggested, then use the following code -
如果您想PDO (PHP Data Object)按照亚历克斯的建议使用，请使用以下代码 -
$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.
}
回答by rvr_jon
Sayem's answer has the most upvotes, but I believe it is incorrect regarding PDO.
Sayem 的回答获得了最多的赞成票，但我认为关于 PDO 是不正确的。
From the PHP docs:
来自PHP 文档：
For most databases, PDOStatement::rowCount() does not return the number of rows affectedby 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.
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() 发出一个 SELECT COUNT(*) 语句，其谓词与您预期的 SELECT 语句相同，然后使用 PDOStatement::fetchColumn() 来检索将返回的行数。
$sql = "SELECT COUNT(*) FROM fruit WHERE calories > 100";
if ($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.";
}
}
$res = null;
$conn = null;
回答by Ilia Choly
another approach
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
}
