PostgreSQL convert varchar to numeric and get average - postgresql

Question

I have a column that I want to get an average of, the column is varchar(200). I keep getting this error. How do I convert the column to numeric and get an average of it.
Values in the column look like
16,000.00
15,000.00
16,000.00 etc
When I execute
select CAST((COALESCE( bonus,'0')) AS numeric)
from tableone
... I get
ERROR: invalid input syntax for type numeric:

Answer 1

The standard way to represent (as text) a numeric in SQL is something like:
16000.00
15000.00
16000.00
So, your commas in the text are hurting you.
The most sensible way to solve this problem would be to store the data just as a numeric instead of using a string (text, varchar, character) type, as already suggested by a_horse_with_no_name.
However, assuming this is done for a good reason, such as you inherited a design you cannot change, one possibility is to get rid of all the characters which are not a (minus sign, digit, period) before casting to numeric:
Let's assume this is your input data
CREATE TABLE tableone
(
bonus text
) ;
INSERT INTO tableone(bonus)
VALUES
('16,000.00'),
('15,000.00'),
('16,000.00'),
('something strange 25'),
('why do you actually use a "text" column if you could just define it as numeric(15,0)?'),
(NULL) ;
You can remove all the straneous chars with a regexp_replace and the proper regular expression ([^-0-9.]), and do it globally:
SELECT
CAST(
COALESCE(
NULLIF(
regexp_replace(bonus, '[^-0-9.]+', '', 'g'),
''),
'0')
AS numeric)
FROM
tableone ;
| coalesce |
| -------: |
| 16000.00 |
| 15000.00 |
| 16000.00 |
| 25 |
| 150 |
| 0 |
See what happens to the 15,0 (this may NOT be what you want).
Check everything at dbfiddle here

Answer 2

I'm going to go out on a limb and say that it might be because you have Empty strings rather than nulls in your column; this would result in the error you are seeing. Try wrapping the column name in a nullif:
SELECT CAST(coalesce(NULLIF(bonus, ''), '0') AS integer) as new_field
But I would really question your schema that you have numeric values stored in a varchar column...