Bug #10633 Precision math: round(x,d) causes truncation if d > 30

• Submitted: 13 May 2005 20:03
• Modified: 3 Apr 2020 16:59
• Reporter: Peter Gulutzan
• Status: Closed
• Category: MySQL Server: Documentation
• Severity: S3 (Non-critical)
• Version: 5.0.6-beta-debug
• OS: Linux (SUSE 9.2)
• Assigned to: Jon Stephens
• CPU Architecture: Any

[13 May 2005 20:03] Peter Gulutzan

Description:
The manual says:
"ROUND(X) , ROUND(X,D) 
Returns the argument X, rounded to the nearest integer. With two arguments, returns X rounded to D decimals."
But if D>30, MySQL rounds as if D=30.
So if I have 35  post-decimal digits and I use ROUND(X,35),
the result has 30 post-decimal digits.

How to repeat:
mysql> select round(.12345678901234567890123456789012345,35);
+------------------------------------------------+
| round(.12345678901234567890123456789012345,35) |
+------------------------------------------------+
| 0.123456789012345678901234567890               |
+------------------------------------------------+
1 row in set (0.00 sec)

[13 May 2005 20:10] MySQL Verification Team

Thank you for the bug report.

[15 Jun 2005 10:00] Alexey Botchkov

Presently we can't support more than 30 digits after the decimal point.
Should be fixed in 5.1.

[29 Sep 2008 21:53] Konstantin Osipov

No reason to keep this not fixed. We should either return an error that 35 digits are not supported, or round correctly.

[9 Nov 2008 14:32] Bugs System

A patch for this bug has been committed. After review, it may
be pushed to the relevant source trees for release in the next
version. You can access the patch from:

  http://lists.mysql.com/commits/58284

2709 Alexey Botchkov	2008-11-09
      Bug#10633 Precision math: round(x,d) causes truncation if d > 30 
              result of the 'DECIMAL' operation was limited with MAX_SCALE.
              But the MAX_SCAL only limits fields of tables, not the 'decimal' engine itself.
              So the limit was changed to MAX_PRECISION.
      
      per-file comments:
        mysql-test/r/func_math.result
      Bug#10633 Precision math: round(x,d) causes truncation if d > 30 
         test result fixed
        mysql-test/r/type_decimal.result
      Bug#10633 Precision math: round(x,d) causes truncation if d > 30 
         test result fixed
        mysql-test/r/type_newdecimal.result
      Bug#10633 Precision math: round(x,d) causes truncation if d > 30 
         test result fixed
        sql/item_func.cc
      Bug#10633 Precision math: round(x,d) causes truncation if d > 30 
         scale limit for decimal operation changed with MAX_PRECISION

[13 Nov 2017 0:41] Federico Razzoli

Still in 8.0.3.

[1 Apr 2020 15:43] Jon Stephens

This is a documentation issue, assigning to myself for resolution.

[3 Apr 2020 16:59] Jon Stephens

The limitation is now noted in all current versions of the Manual.

Closed.