Add a column from a different query for which the value is determined by both a match and a date

Hi Christian,

Not sure if you want Power Query or DAX or what the relationships in your model look like, but as a first draft, DAX, try this...

First Dosing for Subject = 
CALCULATE(
    MIN(Dosing[Collection Time]), 
    FILTER(
        Dosing, 
        Dosing[Study] = 'Adverse Event'[Study] &&
        Dosing[Subject] = 'Adverse Event'[Subject] &&
        'Adverse Event'[Is this a Pre-dose AE?] = "No"
    )
)

Last Dosing Before AE = 
CALCULATE(
    MAX(Dosing[Collection Time]), 
    FILTER(
        Dosing, 
        Dosing[Study] = 'Adverse Event'[Study] &&
        Dosing[Subject] = 'Adverse Event'[Subject] &&
        Dosing[Collection Time] <= 'Adverse Event'[Start Time] && 
        'Adverse Event'[Is this a Pre-dose AE?] = "No"
    )
)

This was done quickly, may need to tweak the calculation a bit.