How to perform pandas column shift in BigQuery?

Question

Lets assume we have a dataset with the following data:

timestamp,col1

1533286270,1
1533286271,2
1533286272,3
1533286273,4
1533286274,5

I want to get preceding col1 value in the col1_prev to be able to compare them. The result should be the same as pandas.shift(-1).

How to achieve this functionality with plain SQL query?

Query result should look like this:

timestamp,col1,col1_prev

1533286270,1,NULL
1533286271,2,1
1533286272,3,2
1533286273,4,3
1533286274,5,4

Answer 1

Using the lag() function is one way:

WITH
  input AS (
  SELECT
    1533286270 AS timestamp,
    1 AS col1
  UNION ALL
  SELECT
    1533286271 AS timestamp,
    2 AS col1
  UNION ALL
  SELECT
    1533286272 AS timestamp,
    3 AS col1
  UNION ALL
  SELECT
    1533286273 AS timestamp,
    4 AS col1
  UNION ALL
  SELECT
    1533286274 AS timestamp,
    5 AS col1 )
SELECT
  timestamp,
  col1,
  LAG(col1) OVER(ORDER BY col1) AS col1_prev
FROM
  input