This articles explores the use of logical expressions in Fabric Dataflows / Power Query. Logical expressions are very useful in Custom Columns and dynamic filtering. The following operators can be used:

OperatorDescription
>Greater than
>=Greater than or equal
<Less than
<=Less than or equal
=Equal
<>Not equal
orConditional logical OR
andConditional logical AND
notLogical NOT

You can use a if – else if expression inside a Custom Column after the each or in any other expression:

let
    varUnitPrice = 120.55,
    varQuantity = 5,
    varLineTotal = varQuantity * varUnitPrice,                  // 602.75

    varOrderLineSize = 
        if      varLineTotal < 100  or  varQuantity = 1     then "Small"
        else if varLineTotal >= 100 and varLineTotal < 500  then "Medium" 
        else if varLineTotal >= 500 and varLineTotal < 1000 then "Large" 
        else    "Extra Large" 
in
    varOrderLineSize                                            // "Large"