如何在 SQL 中将小数四舍五入到最接近的偶数？

Question

I need to round a decimal in a sql query on Oracle 10g to the nearest even number. If the number is even, it should be returned. If the number is odd, the next even number should be returned.

This is what I want: 8.05 should return 8.06, 3.48 should return 3.48

How can I do this?

Thanks, Andrew

Answer 1

If you want to round eg to the second decimal even digit, you can do something like that: select round(3.43 / 0.02, 0) * 0.02; that will produce 3.44 .

This can be extended as you wish: eg first decimal digit which is multiple of 3: select round(3.5452234 / 0.3, 0) * 0.3; will give 3.6 .

Answer 2

I really don't understand the logic of incorrectly rounding numbers. Additionally, this cannot easily because you aren't dealing with integers. However, if you really need to, I would suggest following something like this pseudo-code.

if ((num / 2) * 2 = num) {
    return // number is even
    }
else {
    num = num + .01 // this assumes you are only working with two decimal points.
}

Answer 3

From Oracle Database 18c you can use round_ties_to_even . This rounds the least significant digit for values at the half-way point to the nearest even number.

The first parameter is the value to round. The second is the number of significant digits to round to:

• Zero (the default) => integer rounding
• Positive values => number of digits to the right of the decimal point
• Negative values => number of digits to the left of the decimal point

If all the values have (at most) two decimal places, you can round the hundredths to the nearest even by

• Rounding to two decimal places
• Adding five thousands (0.005) to the input so all values are at the midpoint

For example:

with rws as (
  select 8.04 n from dual union all
  select 8.05 n from dual union all
  select 8.06 n from dual union all
  select 8.07 n from dual union all
  select 3.48 n from dual 
)
  select n, round_ties_to_even ( n + 0.005, 2 )
  from   rws;
  
         N ROUND_TIES_TO_EVEN(N+0.005,2)
---------- -----------------------------
      8.04                          8.04
      8.05                          8.06
      8.06                          8.06
      8.07                          8.08
      3.48                          3.48