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Sqlite 菜鸟在这里。我有一个 SQLite 时间序列数据库，每四分钟更新一次，我想报告最近数据点与（大约）24 小时前的数据点之间的行值差异。如果我跑

SELECT entity_id, state, last_changed
FROM "states" where entity_id = "sensor.nodered_46ce6408_d3dd5c" and last_changed > "1002020-05-14 18:12:28.008172"

我明白了

entity_id   state   last_changed
sensor.nodered_46ce6408_d3dd5c  6940.38     2020-05-04 18:14:35.969094
sensor.nodered_46ce6408_d3dd5c  6940.4      2020-05-04 18:18:45.913404
sensor.nodered_46ce6408_d3dd5c  6940.42     2020-05-04 18:22:55.892357

但是使用以下作为第一步，我什至没有得到最后两个值之间差异的结果。

SELECT entity_id, state, last_changed,
    (SELECT A.state - B.state
        FROM states as B
        WHERE B.entity_id = A.entity_id AND
            B.last_changed = (SELECT MAX(last_changed) FROM states C WHERE C.last_changed > A.last_changed AND C.entity_id = A.entity_id)) AS difference
FROM states as A

我不需要将差异结果写入表中，我只需要每隔几个小时运行一次查询的结果。

解决这个问题的任何线索？TIA。

编辑

我已经改进了我的查询，但还没有。我得到一个接近“选择”：语法错误

SELECT state
    FROM states
    SELECT (A.state - B.state)
    WHERE B.(entity_id = "sensor.nodered_46ce6408_d3dd5c" AND last_changed >= datetime('now', 'localtime','-24 hours') order by last_changed limit 1) AND A.(entity_id = "sensor.nodered_46ce6408_d3dd5c"
    AND last_changed <=  datetime('now', 'localtime') order by last_changed desc limit 1)
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1 回答 1

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有效的答案是：

SELECT b.entity_id, 
       b.state, 
       b.last_changed, 
       ( b.state - (SELECT a.state 
                    FROM   states a 
                    WHERE  a.entity_id = "sensor.nodered_46ce6408_d3dd5c" 
                           AND a.last_changed >= Datetime('now', 'localtime', 
                                                 '-24 hours' 
                                                 ) 
                    ORDER  BY a.last_changed 
                    LIMIT  1) ) AS difference 
FROM   states b 
WHERE  b.entity_id = "sensor.nodered_46ce6408_d3dd5c" 
       AND b.last_changed <= Datetime('now', 'localtime') 
ORDER  BY b.last_changed DESC 
LIMIT  1

感谢@sukitha

于 2020-05-17T13:47:43.473 回答