Compare value between multiple records

So you have a Customer_ID which identifies unique customers, which is great.  What v-yuta-msft is trying to ask is whether you have some ID or index that can be used to determine what order the records for a specific customer would be.

If I ran this query to create a calculated table, how would I know which row was 1st, then 2nd, etc?  Is there an index or other column that indicates the order of records?

TempTable = FILTER(ALL(Table1), [Customer_ID] = "123ABC")

This can be done by date, but it's much easier with an index.  You would want something like this as a calculated column when using date:

QtyUpDown = 
VAR PrevRecordID = CALCULATE( MAX(Table1[Record_ID]), FILTER(Table1, Table1[Customer_ID] = EARLIER(Table1[Customer_ID] && Table1[DateTime]<EARLIER(Table1[DateTime])))
RETURN
IF ( ISBLANK(PrevRecordID), "No previous record", 
    SWTICH( TRUE(),
        Table1[QtyBought] < CALCULATE(SELECTEDVALUE(Table1[QtyBought]), FILTER(ALL(Table1), Table1[Record_ID] = PrevRecordID)), "QTY Went Down",
        Table1[QtyBought] > CALCULATE(SELECTEDVALUE(Table1[QtyBought]), FILTER(ALL(Table1), Table1[Record_ID] = PrevRecordID)), "QTY Went Up",
        Table1[QtyBought] = CALCULATE(SELECTEDVALUE(Table1[QtyBought]), FILTER(ALL(Table1), Table1[Record_ID] = PrevRecordID)), "QTY Stayed Same",
        "Some error occured" )
    )

Replace the section in blue with however you want to determine the order of records.  Note that this will give unintentional results in the case that a customer has two records with the same [DateTime] field - it will calculate them both vs the QTYBought before both.