SQL query reporting what I think is the wrong min value using min aggregate and where operator to filter

Question

I am taking an SQL course on coursera and this question came up on a practice quiz

"Excluding $0.00, what is the minimum bi-weekly high rate of pay (please include the dollar sign and decimal point in your answer)?

Now I got the right answer (Which returned $100.00) using

SELECT 
    min(Biweekly_High_Rate)
FROM
    salary_range_by_job_classification
WHERE Biweekly_High_Rate <> '$0.00'

however, when I query using SELECT * from the same table, I can see that, at least in the rows retrieved, that there is a value of $15.00 which is less than $100.00. Why is it not returning $15.00? table snip of SELECT * FROM salary_range_by_job_classification

Answer 1

I would recommend removing the dollar sign and converting the resultant string to a decimal amount. Enter a decimal amount as your limiting parameter (0.00) as well, so you are comparing two numbers, not two strings. This should result in something more expected:

SELECT MIN(CONVERT(DECIMAL(10,2),REPLACE(BiWeekly_High_Rate,'$','')))
FROM salary_range_by_job_classification
WHERE CONVERT(DECIMAL(10,2),REPLACE(BiWeekly_High_Rate,'$','')) <> 0.00

See how that goes. If you compare two strings, you are asking for (I think) the first value alphabetically by using the MIN aggregation.