Question

I need help with this exercise where I have to translate properties from English into sql.

Questions:

1. length has at least one 0

   Answer: MIN(ABS(length)) = 0
   

2. length has more that one value

   Answer: MIN(length) < MAX(length)
   

3. there are no nulls for length

   Answer: COUNT(*) = COUNT(length)
   

4. values of length are either positive or negative

   Answer: MIN(length) * MAX(length) > 0
   

5. length differs above and below zero by the same amount

   Answer: MIN(length) = -max(length)
   

6. all values of length are different

   Answer: COUNT(DISTINCT length) = COUNT(length)
   

7. only one of min(length) or max(length) is positive

   Answer: MIN(length) * MAX(length) < 0 
   

8. length has one value or null value

   Answer: MIN(length) = MAX(length)
   

Are these correct? I’m not sure about #3, 5, 6 and 8 in particular.

Answer 1

1. length has at least one 0

   Answer: MIN(ABS(length)) = 0
   

2. length has more that one value

   Answer: MIN(length) < MAX(length)
   or
   Answer: COUNT(distinct length) > 1
   

3. there are no nulls for length

   Answer: COUNT(*) = COUNT(length)
   

4. values of length are either positive or negative

   Answer: MIN(length) * MAX(length) > 0
   or
   Better Answer: Sign(MIN(length)) * Sign(MAX(length)) > 0
   
   -- Because, with large values of length, multiplying two of them
   -- together can give you an overflow.
   

5. length differs above and below zero by the same amount

   Answer: MIN(length) = -max(length)
   

6. all values of length are different

   Answer: COUNT(DISTINCT length) = COUNT(length)
   

7. only one of min(length) or max(length) is positive

   Maybe Wrong Answer: MIN(length) * MAX(length) < 0 (0 is not positive)
   or
   Answer: MIN(length) <= 0 and MAX(length) > 0
   
   -- IF: one must be positive and the other must be negative
   -- change <= 0 to < 0
   

8. length has one value or null value

   Wrong Answer: MIN(length) = MAX(length) -- null=null does not return true
   or
   Answer: COUNT(distinct length) <= 1