在第二個查詢中使用查詢結果

Question

我正在嘗試在第二個查詢中將一個查詢的結果用作WHERE的一部分。 我不確定如何最好地解決這個問題，我們將不勝感激：

第一個查詢：

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

第二查詢

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

為了澄清起見，keyword.data_store與keyword.history相關

Answer 1

使用子查詢

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

Answer 2

$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 LIMIT 1");

Answer 3

（因為它無關緊要，所以刪除了PHP方面的內容）

SELECT `id` FROM `data_store` WHERE 
  `keyword` IN (
    SELECT `keyword` FROM `history` ORDER BY `last_update` ASC LIMIT 1
  ) 
ORDER BY `id` DESC LIMIT 1