select a.*,b.* from a left join b on a.k = b.k
select a.*,b.* from a left outer join b on a.k =b.k
----------上面两种一样left join是left outer join的简写
也很及时说：
left join是left outer join的缩写
right join与right outer join的区别也类似
join 与 inner join也类似
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原文链接：https://blog.csdn.net/wyqwilliam/article/details/82709496