Difference between float and decimal data type

mysql
Hacker picture Hacker · Mar 1, 2011 · Viewed 213.3k times · Source

What difference does it make when I use float and decimal data types in MySQL?.

When should I use which?

Answer

kanap008 picture kanap008 · Mar 1, 2011

This is what I found when I had this doubt.

mysql> create table numbers (a decimal(10,2), b float);
mysql> insert into numbers values (100, 100);
mysql> select @a := (a/3), @b := (b/3), @a * 3, @b * 3 from numbers \G
*************************** 1. row ***************************
  @a := (a/3): 33.333333333
  @b := (b/3): 33.333333333333
@a + @a + @a: 99.999999999000000000000000000000
@b + @b + @b: 100

The decimal did exactly what's supposed to do on this cases, it truncated the rest, thus losing the 1/3 part.

So for sums the decimal is better, but for divisions the float is better, up to some point, of course. I mean, using DECIMAL will not give you a "fail proof arithmetic" in any means.

Hope this helps.

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