MySQL问题：子查询不返回结果的内部联接

我有一个数据库，其中包含一组具有不同表单版本的表单。下面的工作查询根据每个表单版本的批准使用日期成功选择最新的表单版本

我想将这个查询工作查询与另一个名为forms\u type的表连接起来，该表返回form\u type列的全文描述

我这样做的尝试不起作用-我应该在查询的连接版本上也得到50个结果，但它没有返回结果

如果有任何帮助或见解，我们将不胜感激，以使我的工作查询正确加入

工作50个结果，但没有连接：

SELECT *
FROM forms AS t
WHERE california =
    ( 
    SELECT MAX(california)
    FROM forms
    WHERE `form_number` = t.`form_number`
    AND trucking_coverage= 1
    AND california IS NOT NULL
    AND california <= '2014-01-29'
    AND form_type <> 0
    )
ORDER BY `t`.`form_type` ASC, `t`.`form_number` ASC

不工作没有结果：

SELECT *
FROM forms AS t
INNER JOIN forms_types 
ON 'forms.form_type' = 'forms_types.form_type'
WHERE california =
    ( 
    SELECT MAX(california)
    FROM forms
    WHERE `form_number` = t.`form_number`
    AND trucking_coverage= 1
    AND california IS NOT NULL
    AND california <= '2014-01-29'
    AND form_type <> 0
    )
ORDER BY `t`.`form_type` ASC, `t`.`form_number` ASC

---

你在找这样的东西吗

SELECT f.*, t.*
  FROM 
( 
  SELECT form_number, MAX(california) california
    FROM forms
   WHERE trucking_coverage = 1
     AND california IS NOT NULL
     AND california <= '2014-01-29'
     AND form_type <> 0
   GROUP BY form_number
) q JOIN forms f
    ON q.form_number = f.form_number
   AND q.california = f.california JOIN forms_types t
    ON f.form_type = t.form_type
 ORDER BY f.form_type, f.form_number

---

您能为forms表显示一个表模式吗？

SELECT *
  FROM
(
  SELECT *
    FROM forms f JOIN forms_types t
      ON f.form_type = t.form_type
   WHERE f.trucking_coverage = 1
     AND f.california IS NOT NULL
     AND f.california <= '2014-01-29'
     AND f.form_type <> 0
   ORDER BY california DESC
) q
 GROUP BY f.form_number
 ORDER BY f.form_type, f.form_number