为什么SQL语句SELECT ROUND（45.926，-1）FROM DUAL print 50

Question

How does dual work? I have executed this with many values Select Round(45.926,-1) from dual it prints 50 while Select Round(45.926,-2) from dual prints 0.

Answer 1

When using ROUND function, the second parameter represents the places after decimal to be taken in result. So, following are results:

SELECT ROUND(45.926) FROM dual;

Result: 46 because no places after decimal to be considered.

SELECT ROUND(45.926, 1) FROM dual;

Result 45.9, consider 1 place after decimal

SELECT ROUND(45.926, -1) FROM dual;

Result: 50, considering the value to be 4.5926, rounding it to 5 and then printing the result.

SELECT ROUND(45.926, -2) FROM dual;

Result: 0, considering the value to be 0.45926, rounding it to 0 and then printing the result in original 10x which is 0x100 = 0.

If you'd taken,

SELECT ROUND(55.926, -2) FROM dual;

Then result will be 100 because it would be like, rounding 0.55926 to 1 and then 10x which 1x100 = 100.

Answer 2

Round(n,m) - rounds the number n to m decimal places.

For m = -1, it rounds the number to tenth place making 45.926 to 50 as it is greater than 45

For m = -2, it rounds the number to 100 place. Since 45.926 is less than 50, it becomes 0. If you try round(51,-2) you should get 100