作业帮select * from a union select * from b 能详细说下么
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select * from a union select * from b 能详细说下么
恩,UNION 跟 UNION ALL 是交集跟并集的写法
select * from a union select * from b --这种是A表与B表结果的交集写法,合并表,没有重复行；
select * from a union all select * from b --这种是A表与B表结果的并集写法 有重复行；
select * from a union select * from b 能详细说下么
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