回答編集履歴
3
追記
test
CHANGED
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@@ -35,3 +35,41 @@
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35
35
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LEFT JOIN FOOD AS FOOD3 ON MENU.REQUIRED_FOOD3= FOOD3.FOOD_ID
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36
36
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37
37
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```
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38
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+
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39
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+
--
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40
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+
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41
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+
相関副問合せで行う。
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42
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+
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43
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+
FOOD_MENU の件数が少なければ（where条件で絞り込まれる場合も含む）こちらの方が高速。
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44
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+
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45
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+
```SQL
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46
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+
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47
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+
SELECT MENU.*
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48
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+
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49
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+
, coalesce(
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50
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+
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51
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+
(select NAME from VEGETABLE_FOOD where FOOD_ID=MENU.REQUIRED_FOOD1)
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52
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+
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53
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,(select NAME from MEAT_FOOD where FOOD_ID=MENU.REQUIRED_FOOD1)
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54
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+
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55
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+
) FOOD1_NAME
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56
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+
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57
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+
, coalesce(
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58
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+
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59
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(select NAME from VEGETABLE_FOOD where FOOD_ID=MENU.REQUIRED_FOOD2)
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60
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+
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61
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+
,(select NAME from MEAT_FOOD where FOOD_ID=MENU.REQUIRED_FOOD2)
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62
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+
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63
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+
) FOOD2_NAME
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64
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+
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65
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+
, coalesce(
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66
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+
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67
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+
(select NAME from VEGETABLE_FOOD where FOOD_ID=MENU.REQUIRED_FOOD3)
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68
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+
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69
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+
,(select NAME from MEAT_FOOD where FOOD_ID=MENU.REQUIRED_FOOD3)
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70
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+
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71
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+
) FOOD3_NAME
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72
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+
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73
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+
FROM FOOD_MENU AS MENU
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74
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+
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75
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+
```
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2
訂正
test
CHANGED
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@@ -26,7 +26,7 @@
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26
26
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27
27
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SELECT MENU.*, FOOD1.NAME, FOOD2.NAME, FOOD3.NAME
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28
28
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29
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-
FROM FOOD_MENU AS
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29
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+
FROM FOOD_MENU AS MENU
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30
30
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31
31
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LEFT JOIN FOOD AS FOOD1 ON MENU.REQUIRED_FOOD1= FOOD1.FOOD_ID
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32
32
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1
追記
test
CHANGED
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@@ -1,3 +1,15 @@
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1
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+
> SQLでJOINするテーブルをカラムの値によって変えたいです。
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2
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+
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3
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+
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4
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+
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5
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+
動的にSQLを組み立てない限りできません。
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6
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+
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7
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+
SQLの基本は集合を作成する事です。ケースがあるなら先ず全ての場合を含んだ集合を作ること。
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8
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+
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9
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+
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10
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+
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11
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+
---
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12
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+
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1
13
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WITH式で纏めて、それを結合
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2
14
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3
15
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```SQL
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