MySQL subtraction between varchar fields returns decimal with too much precision

Question

The following subtraction query returns too many digits after the decimal mark.

mysql> select AA, BB, AA - BB, AA - 23.057,  22.659 - 23.057 from table1 where TID = '1';
+----------+----------+---------------------+---------------------+-----------------+
| AA       | BB       | AA - BB             | AA - 23.057         | 22.659 - 23.057 |
+----------+----------+---------------------+---------------------+-----------------+
| 22.659   | 23.057   | -0.3979999999999997 | -0.3979999999999997 |          -0.398 |
+----------+----------+---------------------+---------------------+-----------------+
1 row in set (0.00 sec)
mysql>

I wish I could use a decimal fields, but the user wants to keep the precision he inserts at input time in the columns AA and BB, that's why VARCHAR is used for those column.

e.g.:  11.10 - 11.22 = - 0.02
       11.20 - 11.10 = + 0.10
       22.659 - 23.057 = -0.398
       23.659 - 22.559 = 0.100

while  23.659 - 22.559 = 0.1 is wrong

Any help would greatly appreciate. Thanks

Answer 1

You can use the format() function:

select format(col1 - col2, length(substring_index(col1, '.', -1)))

If you don't like the commas on larger numbers:

select replace(format(col1 - col2, length(substring_index(col1, '.', -1))), ',', '')