如何使用PHP，PDO，MySQL检查列是否不存在? [英] How to check if column does not exist using PHP, PDO, MySQL?

问题描述

在我的应用程序中，我有一个适用于多个用户的通用查询.在某些情况下，用户之间的表结构可能会有所不同.我有一个查询，我只想将其应用于表中存在该列的用户.

In my application I have a generic query that applies to multiple users. There are instances where the table structure may differ between users. I have a query that I only want to apply to the users where the column exists in their table.

function get_item($user_id) {

    global $dbh;

    $sth = $dbh->query ("SELECT item_type FROM items WHERE user_id = '$user_id'");

    $row = $sth->fetch();

    $item_type = $row['item_type'];

    return $item_type;

}

如果我的表中不存在"item_type"列，我想忽略它，并将$ item_type变量设置为NULL.

If the column 'item_type' does not exist in my table, I want to ignore it, and set the $item_type variable to NULL.

对于这些用户，我在代码查询行上遇到了错误:

For these users, I am getting the error on the query line of code:

致命错误:带有消息的未捕获异常'PDOException' 'SQLSTATE [42S22]:找不到列:1054中的未知列'item_type' /item_display.php:5中的字段列表"

Fatal error: Uncaught exception 'PDOException' with message 'SQLSTATE[42S22]: Column not found: 1054 Unknown column 'item_type' in 'field list' in /item_display.php:5

有什么想法吗?

推荐答案

我不知道它是否对您有帮助，但是您可以尝试以下方法:

I don't know if it helps you, but you can try this:

if (count($dbh->query("SHOW COLUMNS FROM `items` LIKE 'item_type'")->fetchAll())) {
    $sth = $dbh->query ("SELECT item_type FROM items WHERE user_id = '$user_id'");
    $row = $sth->fetch();
    $item_type = $row['item_type'];
} else {
    $item_type = null;
}

它检查该列是否存在并执行任务.

It checks if the column exists and performs the task.

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