Create new column in sql query from CASE expression

I have following sql query:

SELECT score,
    case when index_1<1 THEN target= 0.1+0.01*LEAST(index_1,index_2) ELSE score
END as new_score
FROM new_df

the variable "target" is a new variable that I am trying to create inside my query. as in this query, it returns me an error> no such column: target

How to create this variable inside this query?