How to generate with scripting INTERVAL 1 ?

Question

We are trying to find a syntax to generate the DAY|WEEK|MONTH options from the 3rd param of date functions.

DECLARE var_date_option STRING DEFAULT \'DAY\';
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Answer 1

Below is for BigQuery Standard SQL

Those DAY|WEEK|MONTH are LITERALs and cannot be parametrized
And, as you know - dynamic SQL is also not available yet

So, unfortunately below is the only solution I can think of as of today

#standardSQL
DECLARE var_date_option STRING DEFAULT 'DAY';
DECLARE start_date, end_date DATE;
DECLARE date_array ARRAY<DATE>;

SET (start_date, end_date, var_date_option) = ('2019-01-01','2020-01-01', 'MONTH');

SET date_array = (
  SELECT CASE var_date_option 
    WHEN 'DAY' THEN GENERATE_DATE_ARRAY(start_date, end_date, INTERVAL 1 DAY)
    WHEN 'WEEK' THEN GENERATE_DATE_ARRAY(start_date, end_date, INTERVAL 1 WEEK)
    WHEN 'MONTH' THEN GENERATE_DATE_ARRAY(start_date, end_date, INTERVAL 1 MONTH)
  END
);

SELECT * FROM UNNEST(date_array) AS date_dt;