如果找不到值，则 Foreach 不返回

Question

foreach 如果没有找到，似乎会跳过元素。如果找不到，有没有办法强制它成为 return 备份值？我尝试使用 coalesce 无济于事...如果找到，它将 return period，否则，跳过它并继续检查下一个元素。

$periods = ['October 2021', 'November 2021', 'December 2021'];

foreach ($periods as $k=>$p) {
     $test = $mysqli->query("select coalesce(period, '$p') as period, coalesce(match_date, 'not found') as match_date from table where period = '$p'");  
     while($row = mysqli_fetch_array($test)) {
       echo $row['period']. '-'. $row['match_date']. '<br>'  ;
        } 
    }

Answer 1

首先创建一个 table 然后插入所有带有 foreach

的句点

$reference = $mysqli->query("create temporary table reference (period varchar(15), match_date datetime); ");
foreach ($periods as $k=>$p) {
        $insert = $mysqli->query("insert into reference (period) 
        values ('$p')");
}

然后我使用 left join 和 coalesce

$reference2 = $mysqli->query("select ref.period as period, coalesce(tb.match_date, 'not found') as match_date 
FROM reference as ref 
LEFT JOIN table as tb
ON ref.period = tb.period");

如果找不到值，则 Foreach 不返回

Foreach not returning if value not found

php

mysql