MySQL高级--sql语句

1. sql执行顺序
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sql语句表连接查询（join）

1. • 等值连接：select  * from a inner join b on a.id=b.id;

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   • 左连接：select * from a left join b on a.id=b.id;

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   • 右连接：select * from a right join b on a.id=b.id;

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• • 左连接（变形）：select * from a left join b on a.id=b.id where b.id is NULL;
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  • 有连接（变形）：select * from a right join b on a.id=b.id where a.id is NULL; 

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• • 全连接：select * from a FULL OUTER JOIN b on a.id = b.id;
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    • mysql语句：select * from a left join b where a.id=b.id  union   select * from a right join b where a.id = b.id;
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  • 全连接（变形）：select * from a FULL OUTER JOIN b on a.id= b.if where a.id is NULL or b.id is NULL;
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    • mysql语句：select * from a left join b on a.id= b.id where b.id is null   union  select * from a right join b on a.id= b.id where a.id is null;
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