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select if(a.id is null,b.id,a.id)as id, a.name,a.sex,b.course,b.score from a left join b on a.id=b.id
union
select if(a.id is null,b.id,a.id)as id,a.name,a.sex,b.course,b.score from a right join b on a.id=b.id;
SELECT * FROM A JOIN B