Lag() Function in SQLiteStudio

I am wanting to return the last transaction date grouped by CustomerID, and I am using SQLiteStudio 3.2.1. My table looks like this:

CustomerID   Date       TransactionID    Amount
    1      2000-07-01          1          20.00
    2      2000-07-04          2          40.00
    1      2002-08-01          3          20.00
    1      2007-01-01          4          60.00
    2      2010-05-09          5          70.00
    1      2012-06-25          6          35.00`

This is what I would like the end result to look like: `

CustomerID       Date       TransactionID    Amount  Last Transaction Date
    1          2000-07-01          1          20.00           NULL
    2          2000-07-04          2          40.00           NULL
    1          2002-08-01          3          20.00        2000-07-01
    1          2007-01-01          4          60.00        2002-01-01 
    2          2010-05-09          5          70.00        2000-07-04
    1          2012-06-25          6          35.00`       2007-01-01

I was attempting to use the following code:

SELECT CustomerID, Date, Amount, LAG(Date,1) OVER (PARTITIONED BY CustomerID ORDER BY Date) 
FROM table

However, the lag function is not supported in SQLiteStudio (or maybe I am missing something?). The SQL Editor is also not recognizing the PARTITION BY clause either. Is there a way to use the LAG function or the PARTITION BY clause in the SQL Function Editor? Any help would be greatly appreciated! Thanks!

Also: does anyone have any resources for aggregate function creation in the SQL Function Editor for SQLiteStudio? I know it takes the three parameters of "Initialization code", "Per step code", and "Final step implementation code", but I am looking for examples of the syntax/requirements for these three parameters in SQLiteStudio. (Thanks again!)

Solution

Your partition clause, as your pasted above, has a typo, and it should be PARTITION BY, not PARTITIONED BY. If this be the only problem, then just fix the typo:

SELECT CustomerID, Date, Amount,
       LAG(Date) OVER (PARTITION BY CustomerID
                       ORDER BY Date) AS "Last Transaction Date"
FROM yourTable
ORDER BY Date;

If the above still does not work, then perhaps your version of SQLite does not support LAG. One workaround in this case would be to use a correlated subquery in place of LAG:

SELECT CustomerID, Date, Amount,
       (SELECT t2.Date
        FROM yourTable t2
        WHERE t2.CustomerID = t1.CustomerID AND
              t2.TransactionID < t1.TransactionID
        ORDER BY t2.TransactionID DESC
        LIMIT 1) AS "Last Transaction Date"
FROM yourTable t1
ORDER BY Date;