回答編集履歴
4
推敲
answer
CHANGED
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@@ -48,5 +48,4 @@
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48
48
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left join meter1 ON base.observed= meter1.observed and base.id = meter1.id
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49
49
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left join meter2 ON base.observed= meter2.observed and base.id = meter2.id
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50
50
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left join camera ON base.observed= camera.recorded and base.id = camera.id
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51
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-
```
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51
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+
```
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52
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-
速度的にはhatenaさんの回答の記述の方が早いと思われます。
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3
追記
answer
CHANGED
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@@ -31,4 +31,22 @@
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31
31
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left join mybook2 ON base.id = mybook2.id
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32
32
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left join mybook3 ON base.id = mybook3.id
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33
33
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left join mybook4 ON base.id = mybook4.id
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34
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-
```
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34
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+
```
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35
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+
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36
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+
質問が変更されたので追記
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37
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+
--
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38
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+
```SQL
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39
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+
SELECT base.id, meter1.observed, meter2.observed, camera.recorded
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40
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+
FROM (
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41
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+
select observed, id from (
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42
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+
select observed, id from meter1
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43
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+
union all select observed, id from meter2
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44
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+
union all select recorded, id from camera
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45
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+
) step1
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46
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+
group by observed, id
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47
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+
) base
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48
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+
left join meter1 ON base.observed= meter1.observed and base.id = meter1.id
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49
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+
left join meter2 ON base.observed= meter2.observed and base.id = meter2.id
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50
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+
left join camera ON base.observed= camera.recorded and base.id = camera.id
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51
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+
```
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52
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+
速度的にはhatenaさんの回答の記述の方が早いと思われます。
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2
追記
answer
CHANGED
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@@ -12,4 +12,23 @@
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12
12
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left join mybook2 ON base.id = mybook2.id
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13
13
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left join mybook3 ON base.id = mybook3.id
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14
14
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left join mybook4 ON base.id = mybook4.id
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15
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+
```
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16
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+
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17
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+
以下は冗長になりますが、unionマージでない分高速であるかもしれません。
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18
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+
特にidに対してindexが設定されているようならさらに。
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19
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+
```SQL
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20
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+
SELECT base.id, mybook.name, mybook2.name, mybook3.name, mybook4.name
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21
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+
FROM (
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22
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+
select id from (
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23
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+
select id from mybook
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24
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union all select id from mybook2
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25
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+
union all select id from mybook3
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26
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+
union all select id from mybook4
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27
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+
) step1
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28
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+
group by id
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29
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+
) base
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30
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+
left join mybook ON base.id = mybook.id
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31
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+
left join mybook2 ON base.id = mybook2.id
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32
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+
left join mybook3 ON base.id = mybook3.id
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33
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+
left join mybook4 ON base.id = mybook4.id
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15
34
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```
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1
推敲
answer
CHANGED
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@@ -1,4 +1,4 @@
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1
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-
idを集約するのにfull outerでは無理があります。
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1
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+
idを集約するのに、３つ以上のテーブルでfull outerで行うには無理があります。
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2
2
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一旦全てのIDのリストを取得し、それを元に結合します。
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3
3
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```SQL
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4
4
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SELECT base.id, mybook.name, mybook2.name, mybook3.name, mybook4.name
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