How to generate date series to occupy absent dates in google BiqQuery?

Question

I am trying to get daily sum of sales from a google big-query table. I used following code for that.

select Day(InvoiceDate) date, Sum(InvoiceAmount) sales f         


        

Answer 1

For Standard SQL

WITH

splitted AS (
  SELECT
    *
  FROM
    UNNEST( SPLIT(RPAD('',
          1 + DATE_DIFF(CURRENT_DATE(), DATE("2015-06-01"), DAY),
          '.'),''))),
  with_row_numbers AS (
  SELECT
    ROW_NUMBER() OVER() AS pos,
    *
  FROM
    splitted),
  calendar_day AS (
  SELECT
    DATE_ADD(DATE("2015-06-01"), INTERVAL (pos - 1) DAY) AS day
  FROM
    with_row_numbers)
SELECT
  *
FROM
  calendar_day
ORDER BY
  day DESC

Answer 2

Generting a list of dates and then joining whatever table you need on top seems the easiest. I used the generate_date_array + unnest and it looks quite clean.

To generate a list of days (one day per row):

  SELECT
  *
  FROM 
    UNNEST(GENERATE_DATE_ARRAY('2018-10-01', '2020-09-30', INTERVAL 1 DAY)) AS example

Answer 3

You can use below to generate on fly all dates in given range (in below example it is all dates from 2015-06-01 till CURRENT_DATE() - by changing those you can control which dates range to generate)

SELECT DATE(DATE_ADD(TIMESTAMP("2015-06-01"), pos - 1, "DAY")) AS calendar_day
FROM (
     SELECT ROW_NUMBER() OVER() AS pos, *
     FROM (FLATTEN((
     SELECT SPLIT(RPAD('', 1 + DATEDIFF(TIMESTAMP(CURRENT_DATE()), TIMESTAMP("2015-06-01")), '.'),'') AS h
     FROM (SELECT NULL)),h
)))

so, now - you can use it with LEFT JOIN with your table to have all dates accounted. See potential example below

SELECT
  calendar_day,
  IFNULL(sales, 0) AS sales
FROM (
  SELECT DATE(DATE_ADD(TIMESTAMP("2015-06-01"), pos - 1, "DAY")) AS calendar_day
  FROM (
       SELECT ROW_NUMBER() OVER() AS pos, *
       FROM (FLATTEN((
       SELECT SPLIT(RPAD('', 1 + DATEDIFF(TIMESTAMP(CURRENT_DATE()), TIMESTAMP("2015-06-01")), '.'),'') AS h
       FROM (SELECT NULL)),h
  )))
) AS all_dates
LEFT JOIN (
  SELECT DAY(InvoiceDate) DATE, SUM(InvoiceAmount) sales 
  FROM test_gmail_com.sales 
  WHERE YEAR(InvoiceDate) = YEAR(CURRENT_DATE()) AND
  MONTH(InvoiceDate) = MONTH(CURRENT_DATE())
  GROUP BY DATE 
)
ON DATE = calendar_day  

I wanna need to get previous months sales

Below gives all days of previous month

SELECT DATE(DATE_ADD(DATE_ADD(DATE_ADD(CURRENT_DATE(), -1, "MONTH"), 1 - DAY(CURRENT_DATE()), "DAY"), pos - 1, "DAY")) AS calendar_day
FROM (
     SELECT ROW_NUMBER() OVER() AS pos, *
     FROM (FLATTEN((
     SELECT SPLIT(RPAD('', 1 + DATEDIFF(DATE_ADD(CURRENT_DATE(), - DAY(CURRENT_DATE()), "DAY"), DATE_ADD(DATE_ADD(CURRENT_DATE(), -1, "MONTH"), 1 - DAY(CURRENT_DATE()), "DAY")), '.'),'') AS h
     FROM (SELECT NULL)),h
)))

Answer 4

For these purposes it is practical to have a 'calendar' table, a table that just lists all the days within a certain range. For your specific question, it would suffice to have a table with the numbers 1 to 31. A quick way to get this table is to make a spreadsheet with these numbers, save it as a csv file and import this file into BigQuery as a table.

You then left outer join your result set onto this table, with ifnull(sales,0) as sales.

If you want the number of days per month (28--31) to be right, you basically have two options. Either you create a proper calendar table that covers several years and that you join on using year, month and day. Or you use the simple table with numbers 1--31 and remove numbers based on the month and the year.

Answer 5

Using the Standard SQL dialect and the generate_array function to simplify the code:

WITH serialnum AS (
  SELECT
    sn
  FROM
    UNNEST(GENERATE_ARRAY(0, 
                          DATE_DIFF(DATE_ADD(DATE_TRUNC(CURRENT_DATE()
                                                      , MONTH)
                                          , INTERVAL 1 MONTH)
                                  , DATE_TRUNC(CURRENT_DATE(), MONTH)
                                  , DAY) - 1)
                          ) AS sn
), date_seq AS (
SELECT
    DATE_ADD(DATE_TRUNC(CURRENT_DATE(), MONTH),
            INTERVAL(sn) DAY) AS this_day
FROM
  serialnum
)
SELECT
    Day(InvoiceDate) date
    , Sum(IFNULL(InvoiceAmount, 0)) sales
FROM
    date_seq
    LEFT JOIN
    test_gmail_com.sales
ON
    date_seq.this_day = DAY(test_gmail_com.sales.InvoiceDate)
WHERE
    year(InvoiceDate) = Year(current_date())
    and
    Month(InvoiceDate) = Month(current_date())
GROUP BY
    date
ORDER BY
    date
;

UPDATE

Or, simpler still using the generate_date_array function:

WITH date_seq AS (
SELECT
  GENERATE_DATE_ARRAY(DATE_TRUNC(CURRENT_DATE(), MONTH), 
                      DATE_ADD(DATE_ADD(DATE_TRUNC(CURRENT_DATE(), MONTH)
                                        , INTERVAL 1 MONTH)
                               , INTERVAL -1 DAY)
                      , INTERVAL 1 DAY)
    AS this_day
)
SELECT
    Day(InvoiceDate) date
    , Sum(IFNULL(InvoiceAmount, 0)) sales
FROM
    date_seq
    LEFT JOIN
    test_gmail_com.sales
ON
    date_seq.this_day = DAY(test_gmail_com.sales.InvoiceDate)
WHERE
    year(InvoiceDate) = Year(current_date())
    and
    Month(InvoiceDate) = Month(current_date())
GROUP BY
    date
ORDER BY
    date
;