没有额外的 View ，这个查询一次完成:

SELECT time
      ,COALESCE(temp1
            ,CASE WHEN timediff(time, time1a) > timediff(time1b, time) THEN
                (SELECT t.temperature
                 FROM   temperature_1 t
                 WHERE  t.time = y.time1b)
             ELSE
                (SELECT t.temperature
                 FROM   temperature_1 t
                 WHERE  t.time = y.time1a)
             END) AS temp1

      ,COALESCE(temp2
            ,CASE WHEN timediff(time, time2a) > timediff(time2b, time) THEN
                (SELECT t.temperature
                 FROM   temperature_2 t
                 WHERE  t.time = y.time2b)
             ELSE
                (SELECT t.temperature
                 FROM   temperature_2 t
                 WHERE  t.time = y.time2a)
             END) AS temp2

      ,COALESCE(temp3
            ,CASE WHEN timediff(time, time3a) > timediff(time3b, time) THEN
                (SELECT t.temperature
                 FROM   temperature_3 t
                 WHERE  t.time = y.time3b)
             ELSE
                (SELECT t.temperature
                 FROM   temperature_3 t
                 WHERE  t.time = y.time3a)
             END) AS temp3
FROM  (
  SELECT time
        ,max(t1) AS temp1
        ,max(t2) AS temp2
        ,max(t3) AS temp3

        ,CASE WHEN max(t1) IS NULL THEN
           (SELECT t.time FROM temperature_1 t
            WHERE  t.time < x.time
            ORDER  BY t.time DESC LIMIT 1) ELSE NULL END AS time1a
        ,CASE WHEN max(t1) IS NULL THEN
           (SELECT t.time FROM temperature_1 t
            WHERE  t.time > x.time
            ORDER  BY t.time      LIMIT 1) ELSE NULL END AS time1b
  
        ,CASE WHEN max(t2) IS NULL THEN
           (SELECT t.time FROM temperature_2 t
            WHERE  t.time < x.time
            ORDER  BY t.time DESC LIMIT 1) ELSE NULL END AS time2a
        ,CASE WHEN max(t2) IS NULL THEN
           (SELECT t.time FROM temperature_2 t
            WHERE  t.time > x.time
            ORDER  BY t.time      LIMIT 1) ELSE NULL END AS time2b

        ,CASE WHEN max(t3) IS NULL THEN
           (SELECT t.time FROM temperature_3 t
            WHERE  t.time < x.time
            ORDER  BY t.time DESC LIMIT 1) ELSE NULL END AS time3a
        ,CASE WHEN max(t3) IS NULL THEN
           (SELECT t.time FROM temperature_3 t
            WHERE  t.time > x.time
            ORDER  BY t.time      LIMIT 1) ELSE NULL END AS time3b
  FROM  (
      SELECT time, temperature AS t1, NULL AS t2, NULL AS t3 FROM temperature_1
      UNION ALL
      SELECT time, NULL AS t1, temperature AS t2, NULL AS t3 FROM temperature_2
      UNION ALL
      SELECT time, NULL AS t1, NULL AS t2, temperature AS t3 FROM temperature_3
      ) AS x
  GROUP BY time
  ) y
ORDER BY time;

->sqlfiddle

解释

suqquery x 替换您的 View temptimes 并将温度带入结果。如果所有三个表都同步并且具有所有相同时间点的温度，则甚至不需要其余部分并且速度非常快。
对于三个表中的一个没有行的每个时间点，将按照指示获取温度:从每个表中取出“最接近”的一个。

suqquery y 聚合来自 x 的行并获取上一次 (time1a) 和下一次 (time1b) 根据缺少温度的每个表中的当前时间。使用索引，这些查找应该很快。

最终查询从实际缺失的每个温度的最接近时间的行中获取温度。

如果 MySQL 允许从当前子查询之上的多个级别引用列，则此查询可能会更简单。位它不能。在 PostgreSQL 中工作得很好:->sqlfiddle

如果可以从相关子查询返回多个列，也会更简单，但我不知道如何在 MySQL 中执行此操作。

使用 CTE 和窗口函数会多简单，但是 MySQL 不知道这些现代 SQL 特性(不像其他相关的关系型数据库)。