Question

其实我有以下代码：

$stmt = $pdo->prepare('SELECT id, city, date_created FROM my_table WHERE city = :city ORDER BY date_created DESC LIMIT 1');
$stmt->execute(array(':city' => $city));

我试着解释一下我想做什么：

检查列all中是否有包含city的行。
如果是，请检查date_created中此行的日期是否比上述查询的最新条目中的日期更新。如果是，请选择此行，否则请选择下面查询的最新条目。

我希望你明白我想做什么。不幸的是，我不熟悉SQL中的if / else语句。

有人能帮助我吗？

Answer 1

我认为这可以简化。

看起来您应该只能选择城市是您的参数或“全部”的行，按照date_created的顺序排序，然后选择第一行。

$sql = "SELECT id, city FROM news
        WHERE city IN(:city, 'all')
        ORDER BY date_created DESC LIMIT 1";

由于您知道您的查询只会返回一行，因此您只需使用fetch代替fetchAll来消除不必要的外部数组。

$stmt = $pdo->prepare($sql);
$stmt->execute(array(':city' => $city));
$result = $stmt->fetch(PDO::FETCH_ASSOC);

Answer 2

因为我不熟悉SQL中的if / else语句，但在PHP中我做了以下工作：

<?php
$stmt = $pdo->prepare('SELECT id, city, date_created FROM news WHERE city = :city ORDER BY date_created DESC LIMIT 1');
$stmt->execute(array(':city' => $city));
$results = $stmt->fetchAll();
foreach( $results as $row ) {
$date_city = $row['date_created'];
}
$stmt = $pdo->prepare('SELECT id, city, date_created FROM my_table WHERE city = "all" ORDER BY date_created DESC LIMIT 1');
$stmt->execute();
$results = $stmt->fetchAll();
foreach( $results as $row ) {
$date_all = $row['date_created'];
}
if ($date_all > $date_city) {
$stmt = $pdo->prepare('SELECT id, city, date_created FROM my_table WHERE city = "all" ORDER BY date_created DESC LIMIT 1');
$stmt->execute(array(':city' => $city));
} else {
$stmt = $pdo->prepare('SELECT id, city, date_created FROM my_table WHERE city = :city ORDER BY date_created DESC LIMIT 1');
$stmt->execute(array(':city' => $city));
}
?>

如何在PHP中使用if / else语句和SQL

2 个答案: