Bigquery query performance when using starts_with() on a table of 12Mil rows

Question

I have a table company_totals, that has the following schema -

column_name	column_data_type
company	STRING
link	STRING
full_count	FLOAT
starts_with_count	FLOAT

Number of rows = 12,000,000. Table size = 1.6 GB. CLUSTERED BY = company link. SEARCH INDEX created on column = link.

I have the following select statement which is taking beyond 6 hours and the execution results in timeout - Operation timed out after 6.0 hours. Consider reducing the amount of work performed by your operation so that it can complete within this limit.)

SELECT first_table.company, first_table.link, null as full_count, SUM(second_table.full_count) AS starts_with_count 
FROM company_totals first_table, company_totals second_table 
WHERE STARTS_WITH(second_table.link, first_table.link)
group by first_table.company, first_table.link

The above query calculates values of the column starts_with_count which is the sum of values of another column full_count, based on a starts_with() condition. In the company_totals table, the column starts_with_count is what I want to fill. I have added the expected values for this column manually to show my expectation. Other column values are already present in the table. The starts_with_count value is sum (full_count) where its link appears in other rows.

company	link	full_count	starts_with_count (expected)
abc	http://www.abc.net1	1	15 (= sum (full_count) where link like 'http://www.abc.net1%')
abc	http://www.abc.net1/page1	2	9 (= sum (full_count) where link like 'http://www.abc.net1/page1%')
abc	http://www.abc.net1/page1/folder1	3	3 (= sum (full_count) where link like 'http://www.abc.net1/page1/folder1%')
abc	http://www.abc.net1/page1/folder2	4	4
abc	http://www.abc.net1/page2	5	5
xyz	http://www.xyz.net1/	6	21
xyz	http://www.xyz.net1/page1/	7	15
xyz	http://www.xyz.net1/page1/file1	8	8

Highly appreciate any help in this issue.