php - 在第二个查询中使用查询结果

Question

我正在尝试将一个查询的结果用作第二个查询中 WHERE 的一部分。我不确定如何最好地解决这个问题，非常感谢任何帮助:

第一个查询:

$result = mysql_query("SELECT `keyword` FROM `history` ORDER BY `last_update` ASC LIMIT 1 ");
while($row = mysql_fetch_array($result))
$keyword = $row['keyword'];

第二个查询

$result = mysql_query("SELECT `id` FROM `data_store` WHERE `keyword`= [result from my first query] ORDER BY `id` DESC LIMIT 1");
while($row = mysql_fetch_array($result))
$id = $row['id'];

为了澄清，keyword.data_store 与 keyword.history 相关

Answer 1

使用子查询

$result = mysql_query("
SELECT `id` 
FROM   `data_store` 
WHERE  `keyword` = (SELECT `keyword` 
                    FROM   `history` 
                    ORDER  BY `last_update` ASC 
                    LIMIT  1) 
ORDER  BY `id` DESC");
while($row = mysql_fetch_array($result))
$id = $row['id'];