Stop memorizing every DAX function. These 10 are enough.

1-4: count it right, divide and filter

1. 01

   SUM

   The base measure. Everything builds on it.

   Total Sales = SUM(Sales[Amount])

2. 02

   DISTINCTCOUNT

   Unique customers, not rows.

   Customers = DISTINCTCOUNT(Sales[CustID])

3. 03

   DIVIDE

   Returns blank instead of an error on zero.

   AOV = DIVIDE([Total Sales], [Orders])

4. 04

   CALCULATE

   Same measure, changed filter.

   UP Sales =
   CALCULATE([Total Sales], Store[State] = "UP")

5-8: remove filters, row by row

1. 05

   FILTER

   Row-by-row condition inside CALCULATE.

   Big Orders =
   CALCULATE([Orders],
       FILTER(Sales, Sales[Amount] > 5000))

2. 06

   ALL

   Ignores the slicer for the total. Used for % of total.

   % Share =
   DIVIDE([Total Sales],
       CALCULATE([Total Sales], ALL(Product)))

3. 07

   SUMX

   Multiply per row, then add up.

   Revenue =
   SUMX(Sales, Sales[Qty] * Sales[Price])

4. 08

   RELATED

   Pull a column from the lookup table. Use it in a calculated column on Sales.

   Category = RELATED(Product[Category])

9-10: time and buckets

1. 09

   DATEADD

   Last month's sales. Needs a marked Date table.

   Sales LM =
   CALCULATE([Total Sales],
       DATEADD('Date'[Date], -1, MONTH))

2. 10

   SWITCH(TRUE())

   Cleaner than nested IFs.

   Band =
   SWITCH(TRUE(),
       [Total Sales] > 100000, "High",
       [Total Sales] > 50000, "Mid",
       "Low")

Build these in order. Almost every other measure is CALCULATE([Total Sales], …) with a different filter.