primary key

This paper gives a availability method based on Dependency -matrix that can find all primary attributes and get primary key.

就这类问题的子类给出了一种通过依赖矩阵求出全 部主属性的方法,进而得出主关键字。

Because the coal caving height is larger in fully mechanized top coal caving mining,thick and hard rock strata at higher position turn into the main key stratum,which have large movement and higher impact energy.

综放工作面开采厚度大,高位厚硬岩层会成为主关键层,其运动幅度大、冲击能量高,发生矿震的可能性与危害性加大。

The main key stratum that is made up of the hard stratum covering over the coal seam has a great influence on rock burst.

煤层上覆坚硬厚层岩层组成的主关键层对冲击矿压的发生具有强烈的影响。