Modify values within a column and row (PSQL)

Question

I get the following error for this query: [22P02] ERROR: invalid input syntax for type numeric: "."

select 
date,
row_number () over () as RN,
case when (row_number() over ()) ='8' then '.' else (success/trials) end as "After_1M"
from trials
groupy by date;

Is there another way to indicate that a certain value in a ROWxCOLUMN combination should be adjusted?

Answer 1

Well your description certainly leaves a lot to be desired. But your query only needs slight modification to actually run. First off "groupy by date". I will assume it's just a typo. But a group by without an aggregate function generally doesn't do anything - and this is one of those. But I believe your attempting to get a row count by date. If so the you need the partition by and order by clauses in the in the row_number function. The other issue is in the expression. Each entry in the expression must return the same data type but in case it doesn't. The THEN condition returns character (.) while the ELSE returns a numeric (success/trials) which must define 2 numeric columns to be valid. So which needs to change? I will assume the later. Given this we wind up with:

select date
    , row_number() over(partition by date order by trl_date) rn
    , case when (row_number() over(partition by date order by trl_date)) = 8
           then '.' 
           else (success/trials)::text
      end as  "After_1M"
 from trials;

Note: Date is a very poor date is a very poor column name. It's a reserved word , as well as a data type.