Find Closest Matching Date based on matching ID code from 2 tables

Here is a measure expression that checks start dates in Table 2 before and after the Table 1 start date, and returns the closer one.

Closest Start =
VAR vThisDate =
    MIN ( Table1[Start Date] )
VAR vMinAfter =
    CALCULATE (
        MIN ( Table2[Start_date] ),
        Table2[Start_date] >= vThisDate
    )
VAR vMaxBefore =
    CALCULATE (
        MAX ( Table2[Start_date] ),
        Table2[Start_date] <= vThisDate
    )
RETURN
    IF (
        DATEDIFF (
            vThisDate,
            vMinAfter,
            DAY
        )
            < DATEDIFF (
                vMaxBefore,
                vThisDate,
                DAY
            ),
        vMinAfter,
        vMaxBefore
    )

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