How to extract a piece of string from full length string between two particular positions?

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MySQL

I want take out some string values between two particular positions.
I tried using below query but it did not work out as excepted i used sub_string and position functions.

Please help me on this ..

that indx is a column its values will be like this
Create index index on cust_branch_item_stock_bkp(c_item_code,c_c2code,c_br_code,n_bal_qty,t_ltime,n_rate)


need output:

c_item_code,c_c2code,c_br_code,n_bal_qty,t_ltime,n_rate

What I have tried:

select SUBSTRING(indx,POSITION('(' IN indx)+1,POSITION(')' IN indx)-1) from db_index_list

current output:

c_item_code,c_c2code,c_br_code,n_bal_qty,t_ltime,n_rate)"