我试图将数组的SQL结果转换为字符串，以便在日期变量之间使用变量。然而，我不断收到“类stdClass的对象无法转换为字符串”错误。我尝试过内爆字符串，但一直出现错误。我对内爆的理解是，它将数组变量转换为字符串。

PHP代码（我根据一个查询返回一个较低的日期，该查询根据用户输入的单个日期动态构建日期）：

 <?php
 global $wpdb;
$low_date = $wpdb->get_results("SELECT low_date FROM (SELECT low_date FROM (SELECT @row:=0) temp, (select * from (select adddate((SELECT main.date FROM (SELECT DATE_FORMAT((CONCAT(starting_deposit_dt_yy, \'-\', starting_deposit_dt_mm, \'-\', starting_deposit_dt_dd)), \'%Y-%m-%d\') AS `date`  FROM income WHERE user_id = $user_id) AS main) ,t4.i*10000 + t3.i*1000 + t2.i*100 + t1.i*10 + t0.i) low_date from (select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t0, (select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t1, (select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t2, (select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t3, (select 0 i union select 1 union select 2 union select 3 union select 4 union select 5 union select 6 union select 7 union select 8 union select 9) t4) v where low_date between (SELECT DATE_FORMAT((CONCAT(starting_deposit_dt_yy, \'-\', starting_deposit_dt_mm, \'-\', starting_deposit_dt_dd)), \'%Y-%m-%d\') FROM income where user_id = $user_id) and DATE_ADD(DATE(SYSDATE()), INTERVAL 365 DAY)) d WHERE (@row:=@row + 1) % 14 = 1 ORDER BY low_date ASC) s WHERE low_date <= DATE(SYSDATE()) ORDER BY low_date DESC LIMIT 1");
foreach($low_date as $row) {
    echo $row->low_date;
}

?>

查询返回我需要的正确日期。打印$low\\u日期时，我得到：

Array ( [0] => stdClass Object ( [low_date] => 2020-02-21 ) )

我试图在查询中使用$low\\u date和$high\\u date（未显示）来查看日期字段：

<?php
 $table_name = "accounts";
 $results = $wpdb->get_results ( "SELECT * FROM (
SELECT account_name, current_balance, minimum_due, last_pmt_amt, DATE_FORMAT((CONCAT(next_pmt_dt_yy, \'-\', next_pmt_dt_mm, \'-\', due_day)), \'%Y-%m-%d\') AS next_pmt_dt, autopay, status, account_type, url FROM accounts) vwd
WHERE user_id = $user_id AND vwd.next_pmt_dt BETWEEN \'$low_date\' AND \'$high_date\' ORDER BY next_pmt_dt ASC" ); // Query to fetch data from database table and storing in $results
 if(!empty($results))   // Checking if $results have some values or not
 {
    echo "<table width=\'100%\' border=\'1\'>";   // Adding <table> and <tbody> tag outside foreach loop so that it wont create again and again
    echo  \'<tr>\';  //This prevents duplicate rows for header records since it\'s above the loop
    echo \'<th>Account</th>\';
    echo \'<th>Balances</th>\';
    echo \'<th>Min Due</th>\';
    echo \'<th>Last Payment Amount</th>\';
    echo \'<th>Next Payment Date</th>\';
    echo \'<th>Autopay</th>\';
    echo \'<th>Status</th>\';
    echo \'<th>Type</th>\';
    echo \'<th>URL</th>\';
    echo \'<th>Action</th>\';
    echo \'</tr>\';
    echo "<tbody>";      

    foreach($results as $row){   
  //  $user_id = $row->user_id;               //putting the user_id field value in variable to use it later in update query
      echo \'<td>\' . $row->account_name.\'</td>\';
      echo \'<td>\' . $row->current_balance.\'</td>\';
      echo \'<td>\' . $row->minimum_due.\'</td>\';
      echo \'<td>\' . $row->last_pmt_amt.\'</td>\';
      echo \'<td>\' . $row->next_pmt_dt.\'</td>\';
      echo \'<td>\' . $row->autopay.\'</td>\';
      echo \'<td>\' . $row->status.\'</td>\';
      echo \'<td>\' . $row->account_type.\'</td>\';
      echo \'<td>\' . "<a target=\\"_blank\\" href=" .  $row->url. ">LINK</a>".\'</td>\';
      echo \'<td>\' . "<a target=\\"_blank\\" href=" .  $row->url. ">UPDATE</a>".\'</td>\';
      echo \'</tr>\';
    }
        echo "</tbody>";
    echo "</table>"; 
 }

当我硬编码日期时，查询在PHPmyAdmin中按预期工作，并且在打印变量时可以看到返回的正确日期，因此我认为我的问题是需要将数组转换为字符串。

在$low\\u日期的初始注册下方，我尝试将其内爆：

$low_date_str = implode($low_date);

然后我每次都会收到错误。

我错过了什么？我对PHP有点陌生，所以我可能只是缺少一些简单的东西。

Update: Tom帮助我理解了我需要将数组的值（总是以单键数组的形式返回）传递给一个新字符串，但由于对PHP来说有点陌生，我不确定如何检索数组键的值。

$low_date_str = $low_date[0]->low_date;
$high_date_str = $high_date[0]->high_date;

检索键并将其传递给新变量以在SQL中使用时，我只需要这些代码。再次感谢你，汤姆！