How to find missing dates in BigQuery table using sql - google-cloud-platform

Question

How to get a list of missing dates from a BigQuery table. For e.g. a table(test_table) is populated everyday by some job but on few days the jobs fails and data isn't written into the table.

Answer 1

Use Case:
We have a table(test_table) which is populated everyday by some job( a scheduled query or cloud function).Sometimes those job fail and data isn't available for those particular dates in my table.
How to find those dates rather than scrolling through thousands of rows.
The below query will return me a list of dates and ad_ids where data wasn't uploaded (null).
note: I have used MAX(Date) as I knew dates was missing in between my boundary dates. For safe side you can also specify the starting_date and ending_date incase data hasn't been populated in the last few days at all.
WITH Date_Range AS
-- anchor for date range
(
SELECT MIN(DATE) as starting_date,
MAX(DATE) AS ending_date
FROM `project_name.dataset_name.test_table`
),
day_series AS
-- anchor to get all the dates within the range
(
SELECT *
FROM Date_Range
,UNNEST(GENERATE_TIMESTAMP_ARRAY(starting_date, ending_date, INTERVAL 1 DAY)) AS days
-- other options depending on your date type ( mine was timestamp)
-- GENERATE_DATETIME_ARRAY or GENERATE_DATE_ARRAY
)
SELECT
day_series.days,
original_table.ad_id
FROM day_series
-- do a left join on the source table
LEFT JOIN `project_name.dataset_name.test_table` AS original_table ON (original_table.date)= day_series.days
-- I only want the records where data is not available or in other words empty/missing
WHERE original_table.ad_id IS NULL
GROUP BY 1,2
ORDER BY 1
Final output will look like below:

Answer 2

An Alternate solution you can try following query to get desired output:-
with t as (select 1 as id, cast ('2020-12-25' as timestamp) Days union all
select 1 as id, cast ('2020-12-26' as timestamp) Days union all
select 1 as id, cast ('2020-12-27' as timestamp) Days union all
select 1 as id, cast ('2020-12-31' as timestamp) Days union all
select 1 as id, cast ('2021-01-01' as timestamp) Days union all
select 1 as id, cast ('2021-01-04' as timestamp) Days)
SELECT *
FROM (
select TIMESTAMP_ADD(Days, INTERVAL 1 DAY) AS Days, TIMESTAMP_SUB(next_days, INTERVAL 1 DAY) AS next_days from (
select t.Days,
(case when lag(Days) over (partition by id order by Days) = Days
then NULL
when lag(Days) over (partition by id order by Days) is null
then Null
else Lead(Days) over (partition by id order by Days)
end) as next_days
from t) where next_days is not null
and Days <> TIMESTAMP_SUB(next_days, INTERVAL 1 DAY)),
UNNEST(GENERATE_TIMESTAMP_ARRAY(Days, next_days, INTERVAL 1 DAY)) AS days
Output will be as :-

Answer 3

I used the code above but had to restructure it for BigQuery:
-- anchor for date range - this will select dates from the source table (i.e. the table your query runs off of)
WITH day_series AS(
SELECT *
FROM (
SELECT MIN(DATE) as starting_date,
MAX(DATE) AS ending_date
FROM --enter source table here--
---OPTIONAL: filter for a specific date range
WHERE DATE BETWEEN 'YYYY-MM-DD' AND YYYY-MM-DD'
),UNNEST(GENERATE_DATE_ARRAY(starting_date, ending_date, INTERVAL 1 DAY)) as days
-- other options depending on your date type ( mine was timestamp)
-- GENERATE_DATETIME_ARRAY or GENERATE_DATE_ARRAY
)
SELECT
day_series.days,
output_table.date
FROM day_series
-- do a left join on the output table (i.e. the table you are searching the missing dates for)
LEFT JOIN `project_name.dataset_name.test_table` AS output_table
ON (output_table.date)= day_series.days
-- I only want the records where data is not available or in other words empty/missing
WHERE output_table.date IS NULL
GROUP BY 1,2
ORDER BY 1