SWITCH function considering zeros and blanks

See explanation below, taken form https://www.sqlbi.com/articles/blank-handling-in-dax/

The behavior change only kicks in when BLANK is casted to a Boolean value in DAX. When the original column is already of Boolean data type, there is no cast, hence BLANK is preserved.

SWITCH can be rewritten as nested IF, so we only need to consider IF function.

When the two branches of IF have two different data types, IF returns variant data type. Since calculated column is always strongly typed, it raises error if the underlying DAX expression is of variant data type.

BLANK value by itself can be treated as of any (undefined) data type, so IF (<condition>, <expression>, BLANK) and IF (<condition>, BLANK, <expression>) are treated as the data type of <expression>. When <expression> is of Boolean data type, IF is of Boolean data type and an implicit cast is applied to BLANK which converts to FALSE.

BLANK here is being evaluated as FALSE which is the same as 0, so your IF function will evailatue BLANK and 0 as 0.

ISBLANK function differs slightly, and is written specifically to not cast 0s to BLANK().

So:

BLANK() = 0 = true

ISBLANK(0)= FALSE

That's why it will evaluate both as 1. Interestingly if you rewrote:

SWITCH(TRUE(), ISBLANK(measure), 2, measure = 0, 1)

as:

SWITCH(TRUE(), , measure = 0, 1,ISBLANK(measure), 2)

this would evaluate everything as 1, as it would check for 0s first, which it would cast the blank to 0.

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You can force the compare to not consider the BLANK as 0 by using the new Strict equal to operator ==

SWITCH(TRUE(),
measure == 0, 1,
ISBLANK(measure), 2)

will work the way you wanted.