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
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）
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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