sql語句優化

正常sql語句順序：select-from- join on- where-group by-having-order by -limit join語句：inner join 取公共有部分   left join 取左表的獨有和兩表的共有  right join 取右表的獨有和兩表的共有 select *from a left join b on a.key=b.key where b.key i

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