回答編集履歴
1
sample
test
CHANGED
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@@ -3,3 +3,93 @@
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3
3
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leftなら左、rightなら右を基準に合致させて、基準側は
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4
4
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5
5
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余れば放置、joinする側は余れば削除する・・・感じです
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6
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+
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7
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+
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8
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+
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9
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# sample
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10
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+
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11
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※以下サンプル上げておきます。
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12
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+
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13
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書式はmysqlなのでご自身の環境あわせて適宜調整ください
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14
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+
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15
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```SQL
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16
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17
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create table tbl_left(id int primary key,num int,val int);
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18
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+
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19
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insert into tbl_left values
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20
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21
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(1,1,100),
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22
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23
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(2,1,101),
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24
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25
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(3,2,200),
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26
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27
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(4,2,201),
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28
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29
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(5,3,300);
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30
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31
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32
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33
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create table tbl_right(id int primary key,num int,val int);
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34
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35
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insert into tbl_right values
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36
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37
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(11,1,110),
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38
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39
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(12,1,111),
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40
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41
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(13,1,112),
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42
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43
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(14,3,310),
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44
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45
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(15,4,410);
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46
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47
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```
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48
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+
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49
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上記に対して以下実行すると
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50
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51
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```SQL
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52
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53
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select * from tbl_left as l
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54
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55
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left join tbl_right as r
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56
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57
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on l.num=r.num
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58
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59
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order by l.id asc,r.id asc
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60
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61
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```
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62
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63
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leftテーブルのidは全て生き、rightテーブルのid=15は削除されています
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64
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65
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逆に、以下だと
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66
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67
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```SQL
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68
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69
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select * from tbl_left as l
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70
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71
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right join tbl_right as r
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72
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73
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on l.num=r.num
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74
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75
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order by l.id asc,r.id asc
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76
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77
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```
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78
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79
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leftテーブルのid=3,4は削除され、rightテーブルのidはすべて生きます
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80
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81
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ちなみにinner joinすれば
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82
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83
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```SQL
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84
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85
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select * from tbl_left as l
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86
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87
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inner join tbl_right as r
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88
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89
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on l.num=r.num
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90
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91
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order by l.id asc,r.id asc
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92
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93
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```
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94
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95
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行き場のないleftのid=13,14やrightのid=15が削除されます
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