我现在手上有两个数据表，traffic和es。想把这两个表通过共同的变量region合并起来。我输入的命令是：merge 1:1 region using traffic。一直提示错误是：variable region does not uniquely identify observations in the master datar(459);
        Keywords:  r(459)
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[P]     error . . . . . . . . . . . . . . . . . . . . . . . .  Return code 459
        something that should be true of your data is not;
        data have changed since estimation;
        This is the generic form of this message; more likely, you
        will see messages such as "y must be between 0 and 1" or
        "x not positive".  You have attempted to do something that,
        given your data, does not make sense.


刚开始接触stata软件，不是很懂到底哪里出了问题...
有朋友可以帮帮忙吗？