Re: mysql float data type
From: Lucio Chiappetti lu...@lambrate.inaf.it never used DECIMAL nor intend to Why would you blow off an important feature of any system? DECIMAL performs infinite precision math, and should be used in ALL situations where you don't want rounding errors. It should ALWAYS be your first choice for quantities of money, for example. If a taxpayer thinks he can cheat safely, he probably will. -- Diogenes Jan Steinman, EcoReality Co-op -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe:http://lists.mysql.com/mysql
Re: mysql float data type
On Tue, 16 Dec 2014, Hartmut Holzgraefe wrote: On 16.12.2014 15:16, xiangdongzou wrote: Can anyone tell me why 531808.11 has been changed to 531808.12 ? typical decimal-binary-decimal conversion/rounding error. never used DECIMAL nor intend to, but the issue is typical of precision issues among float (32-bit) and double (64-bit) in ANY programming language. Google for IEEE floating point Some (most) users are unaware that a 32-bit real (REAL*4 for oldtimer Fortran users like myself) have about 7 digits of precision, while 64-bit (doubles, double precision, REAL*8) get to about 16. So if a quantity needs high precision (typically this occurs for angular quantities where arcseconds are important), use double. -- Lucio Chiappetti - INAF/IASF - via Bassini 15 - I-20133 Milano (Italy) For more info : http://www.iasf-milano.inaf.it/~lucio/personal.html Do not like Firefox =29 ? Get Pale Moon ! http://www.palemoon.org -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe:http://lists.mysql.com/mysql
Re: mysql float data type
We always store as strings to avoid rounding issues and then convert for calcs to whatever precision we need. Pat... Sent from my iPhone On Dec 17, 2014, at 6:24 AM, Lucio Chiappetti lu...@lambrate.inaf.it wrote: On Tue, 16 Dec 2014, Hartmut Holzgraefe wrote: On 16.12.2014 15:16, xiangdongzou wrote: Can anyone tell me why 531808.11 has been changed to 531808.12 ? typical decimal-binary-decimal conversion/rounding error. never used DECIMAL nor intend to, but the issue is typical of precision issues among float (32-bit) and double (64-bit) in ANY programming language. Google for IEEE floating point Some (most) users are unaware that a 32-bit real (REAL*4 for oldtimer Fortran users like myself) have about 7 digits of precision, while 64-bit (doubles, double precision, REAL*8) get to about 16. So if a quantity needs high precision (typically this occurs for angular quantities where arcseconds are important), use double. -- Lucio Chiappetti - INAF/IASF - via Bassini 15 - I-20133 Milano (Italy) For more info : http://www.iasf-milano.inaf.it/~lucio/personal.html Do not like Firefox =29 ? Get Pale Moon ! http://www.palemoon.org -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe:http://lists.mysql.com/mysql -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe:http://lists.mysql.com/mysql
Re: mysql float data type
On 17 December 2014 14:21:40 CET, Patrick Sherrill patr...@michael-clarke.com wrote: We always store as strings to avoid rounding issues and then convert for calcs to whatever precision we need. Pat... So you'll still be affected by rounding errors during conversion and calculation, two problems you'd avoid when using DECIMAL instead ... -- Hartmut Holzgraefe, Principal Support Engineer (EMEA) MariaDB Corporation | http://www.mariadb.com/ -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe:http://lists.mysql.com/mysql
mysql float data type
HI everyone: I have created a table as flowing; create table t1(c1 float(10,2), c3 decimal(10,2)); insert two records insert into t1 values(531808.11, 9876543.12); insert into t1 values(531808.81, 9876543.12); the result is mysql select * from t1; +---++ | c1| c3 | +---++ | 531808.12 | 9876543.12 | | 531808.81 | 9876543.12 | +---++ Can anyone tell me why 531808.11 has been changed to 531808.12 ? 2014-12-16 I AM AN ORACLE FANS! Skype:Frank.oracle Email:xiangdong...@gmail.com Name:东东堂
Re: mysql float data type
On 16.12.2014 15:16, xiangdongzou wrote: Can anyone tell me why 531808.11 has been changed to 531808.12 ? typical decimal-binary-decimal conversion/rounding error. If you want exact decimals you need to stick with the DECIMAL type which doesn't have this problem, at the cost of slower calculations though. see also: http://dev.mysql.com/doc/refman/5.5/en/problems-with-float.html -- Hartmut Holzgraefe, Principal Support Engineer (EMEA) MariaDB Corporation | http://www.mariadb.com/ -- MySQL General Mailing List For list archives: http://lists.mysql.com/mysql To unsubscribe:http://lists.mysql.com/mysql
