Convert String to Tuple in BigQuery - sql

Question

I have a variable passed as an argument in BigQuery which is in the format "('a','b','c')"
with vars as (
select "{0}" as var1,
)
-- where, {0} = "('a','b','c')"
To use it in BigQuery I need to make it a tuple ('a','b','c').
How can it be done?
Any alternate approach is also welcome.
Example:
with vars as (
select "('a','b','c')" as index
)
select * from `<some_other_db>.table` where index in (
select index from vars)
-- gives me empty results because index is now a string
Present output:
select * from <db_name>.table where index in "('a','b','c')"
Required output:
select * from <db_name>.table where index in ('a','b','c')

Answer 1

Below is for BigQuery Standard SQL
#standardSQL
WITH vars AS (
SELECT "('a','b','c')" AS var
)
SELECT *
FROM `<some_other_db>.table`
WHERE index IN UNNEST((
SELECT SPLIT(REGEXP_REPLACE(var, r'[()\']', ''))
FROM vars
))
You can test, play with above using some dummy data as in below example
#standardSQL
WITH vars AS (
SELECT "('a','b','c')" AS var
), `<some_other_db>.table` AS (
SELECT 1 id, 'a' index UNION ALL
SELECT 2, 'd' UNION ALL
SELECT 3, 'c' UNION ALL
SELECT 4, 'e'
)
SELECT *
FROM `<some_other_db>.table`
WHERE index IN UNNEST((
SELECT SPLIT(REGEXP_REPLACE(var, r'[()\']', ''))
FROM vars
))
with output
Row id index
1 1 a
2 3 c

Answer 2

I think this does what you are asking for:
with vars as ( select "('a','b','c')" as var1)
select as struct
MAX(CASE WHEN n = 0 then var END) as f1,
MAX(CASE WHEN n = 1 then var END) as f2,
MAX(CASE WHEN n = 2 then var END) as f3
from vars v cross join
unnest(SPLIT(REPLACE(REPLACE(var1, '(', ''), ')', ''), ',')) var with offset n;