• mysql手册里边的 P(T1,T2) 是什么意思

    02/03 、O.o? 3 评论

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  • Kenneth hired worker 02/06

    It means that

    R(T2) is conditions. You set many conditions to narrow rows from Table2. for example :

     The point is that you can optimize your query. 

    From

    to

    PS: please attached the link next time. Who know what mysql手册 is

    https://dev.mysql.com/doc/refman/5.5/en/outer-join-simplification.html