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  • 内连接自连接和内嵌自连接的区别

     select (SELECT count(1)FROM  entity.PhysicalItemResult sub,entity.PhysicalItemResult main
    WHERE sub.physicalitemid = main.physicalitemid  AND sub.physicalitemresultid <= main.physicalitemresultid
    ) as '序号',physicalitemid,physicalitemresultid
    from entity.PhysicalItemResult
    -------------------------------
    SELECT(SELECT COUNT(1) FROM entity.PhysicalItemResult sub WHERE sub.physicalitemid = main.physicalitemid
    AND sub.physicalitemresultid <= main.physicalitemresultid) AS 序号,physicalitemid,physicalitemresultid
    FROM entity.PhysicalItemResult main

    为什么第二次数据是这样?内嵌,

    每一对main的physicalitemid,physicalitemresultid就对应一次嵌套查询(循环嵌套?)
     

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  • 原文地址:https://www.cnblogs.com/xiaotan/p/2790790.html
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