In addition, if you have a table with many columns that aren't typically used, you are also wasting disk space with NULL value fields.

此外，如果您有不常用的含多个列的一个表，您也在通过null值字段浪费磁盘空间。

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Enter a space if you want a value to be null.

如果您想要一个值为空，可以输入一个空格。

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Beam pattern null in the direction of the jamming is formed by a space filtering and assisted receive channels to suppress the jamming.

它是采用空间滤波技术，通过辅助通道在干扰方向上形成波束图的零点来实现对干扰信号的抑制。

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