回答編集履歴
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sample
answer
CHANGED
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product_idに対してmail_typeの1,3が固定なら正規化するのが普通です
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1
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product_idに対してmail_typeの1,3が固定なら正規化するのが普通です
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2
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3
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# sample
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4
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```SQL
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5
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create table products(product_id int unique,name varchar(10));
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6
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insert into products values
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7
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(1,'test1'),(2,'test2'),(4,'test4');
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8
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9
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create table mail_products(product_id int unique);
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10
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insert into mail_products values(1),(3),(5);
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11
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12
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create table types(mail_type int unique);
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13
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insert into types values(1),(3);
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14
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15
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select * from mail_products,types;
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16
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```
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17
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ここでmail_productsに対してproductsのデータを流し込んで再表示
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18
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```SQL
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19
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insert ignore into mail_products select product_id from products;
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20
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21
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select * from mail_products,types;
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22
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```
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