select a.*, b.* from a inner join b on a1=b1 and a2=b2 and a3=b3
select a.*, b.* from a left join b on a1=b1 where a2=b2 and a3=b3
select a.*, b.* from a left join b on a1=b1 and a2=b2 and a3=b3
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