Bug #84449 Signed zero not preserved by mysqldump/restore

• Submitted: 9 Jan 2017 19:08
• Modified: 9 Jan 2017 20:48
• Reporter: Hartmut Holzgraefe
• Status: Verified
• Category: MySQL Server: mysqldump Command-line Client
• Severity: S3 (Non-critical)
• Version: 5.5/5.6/5.7/8.0
• OS: Any
• CPU Architecture: Any

[9 Jan 2017 19:08] Hartmut Holzgraefe

Description:
It is possible to insert negative signed zero into a FLOAT column in several different ways:

* INSERT(0) and INSERT(-0) both insert a positive 0
* INSERT('-0'), INSERT(-0e0) and INSERT(ROUND('-0.1')) all insert a negative signed 0

mysqldump dumps 0 and -0 correctly, but as the values are not quoted they are both restored as positive 0

How to repeat:
CREATE TABLE t1(x double);

INSERT INTO t1 VALUES (0e0),(-0e0);

SELECT x FROM t1;
+------+
| x    |
+------+
|    0 |
|   -0 |
+------+

... do mysqldump

... restore from mysqldump

SELECT x FROM t1;
+------+
| x    |
+------+
|    0 |
|    0 | <- expected -1 here
+------+

Suggested fix:
check for literal "-0" in mysqldump when processing field values for INSERT output, add quotes or convert to -0e0 in such cases to preserve zero signednes

[9 Jan 2017 20:48] MySQL Verification Team

Thank you for the bug report. Verified as described.