How to get difference between consecutive rows in BigQuery

We have a series of entries in a database, one of which is a timestamp. I'd like to add as a field the difference between the Values of the current row and the row preceding it.

This is the table:

Row No	Date	Values
1	2012-10-30	10245
2	2012-10-31	25416
3	2012-11-01	84252
4	2012-11-02	21454
5	2012-11-03	54436
6	2012-11-04	49364
7	2012-11-05	42656

This is the result we need:

Row No	Date	Values	Pre-Value	Diffrence
1	2012-10-30	10245	-
2	2012-10-31	25416	10245	15171
3	2012-11-01	84252	25416	58836
4	2012-11-02	21454	84252	-62798
5	2012-11-03	54436	21454	32982
6	2012-11-04	49364	54436	-5072
7	2012-11-05	42656	49364	-6708

Syntax:-

Lag() over (order by )

For Example:-

Select 
Date,
Values ,
lag(Values) over (order by date) as Pre_value
From
[project.dataset.table]

We get Output as :

Row No	Date	Values	Pre-Value
1	2012-10-30	10245	-
2	2012-10-31	25416	10245
3	2012-11-01	84252	25416
4	2012-11-02	21454	84252
5	2012-11-03	54436	21454
6	2012-11-04	49364	54436
7	2012-11-05	42656	49364

Now we want to calculate diffrence:

Select 
Date,
Values ,
lag(Values) over (order by date) as Pre_value,
(Values-Pre_values) as Difference
From
[project.dataset.table]

we get final out-put as:

Row No	Date	Values	Pre-Value	Diffrence
1	2012-10-30	10245	-
2	2012-10-31	25416	10245	15171
3	2012-11-01	84252	25416	58836
4	2012-11-02	21454	84252	-62798
5	2012-11-03	54436	21454	32982
6	2012-11-04	49364	54436	-5072
7	2012-11-05	42656	49364	-6708