桥接表-DAX还是M？ [英] Bridge tables - DAX or M?

问题描述

我们应该用DAX或M构造桥表吗？

Should we construct bridge tables with DAX or M?

从此处

使用DAX似乎很诱人。使用DAX，代码简短明了：

It seems very tempting to use DAX. With DAX the code is short and clear:

IDList = DISTINCT(
    UNION(
         DISTINCT(Table1[ID]) 
        ,DISTINCT(Table2[ID])
        ))

此外，DAX表不必作为M表加载。但是我想知道DAX相对于M的优势是否不是虚幻的？ M似乎加载一次并且DAX似乎是一次又一次地动态计算？

Moreover, DAX tables do not need to be loaded as M tables. However I wonder if advantage of DAX over M is not illusory? M seems to load once and DAX seems to be calculated on the fly, maybe anytime, over and over?

推荐答案

DAX计算表如果从其中提取数据的任何表以任何方式刷新或更新，都将重新计算。 （来自 https://docs.microsoft.com/zh- us / power-bi / desktop-calculated-tables ）

DAX calculated tables are re-calculated if any of the tables it pulls data from are refreshed or updated in any way. (from https://docs.microsoft.com/en-us/power-bi/desktop-calculated-tables )

它们不会即时重新计算，也不会反复计算 。使用DAX计算表或M查询表，Power BI数据模型的刷新周期没有区别。但是，您可能会发现，根据表的复杂程度，DAX计算的表的刷新速度比M快。

They're not re-calculated "on the fly", nor "over and over". There's no difference to the refresh cycle of your Power BI data model, between using a DAX calculated table or an M query table. You may however find that DAX calculated tables refresh faster than M, depending on the complexity of the table...

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