MySQL Bugs: #12336: "DECIMAL ADD DECIMAL" RESULT A NON EXACT NUMRIC?

Bug #12336	"DECIMAL ADD DECIMAL" RESULT A NON EXACT NUMRIC?
Submitted:	3 Aug 2005 7:34	Modified:	3 Aug 2005 8:38
Reporter:	tony chen	Email Updates:
Status:	Not a Bug	Impact on me:	None
Category:	MySQL Server	Severity:	S3 (Non-critical)
Version:	4.1.13	OS:	Linux (Mandrike Linux 8.1)
Assigned to:		CPU Architecture:	Any

Description:
I dowload  LINUX X86 RPM PACKAGES(4.1.13-0 ,11.7M) , AND INSTALL IT.
I find some problem when compute two decimal type number.
these problem are not occur in MySQL 4.1.5

How to repeat:
1.
CREATE TABLE TEST (
     T_1 INT NOT NULL,
     N_1 DECIMAL(10,2) NOT NULL,
     N_2 DECIMAL(10,2) NOT NULL,
     PRIMARY KEY (T_1)
)

2.  INSERT INTO TEST VALUES (1, 1.10,      -1.10)
     INSERT INTO TEST VALUES (2, 1605.00, -1605.00)
     INSERT INTO TEST VALUES (3, 338.70,   -338.70)

3.  SELECT * ,N_1+N_2 FROM TEST WHERE N_1 + N_2 <>0  (WRONG)

T1         N_1          N_2          N_1+N_2
----------------------------------------
1          1.10         -1.10         0.00
3        338.70     -338.70       -0.00

4.  SELECT * FROM TEST WHERE N_1<> -1 * N_2  (CORRECT)

T1         N_1          N_2
----------------------------------- 
NONE

Tony,

Prior to MySQL 5.0.3, decimal values could have up to 254 digits. However, calculations were done using floating-point and thus were approximate, not exact.

Since 5.0.3 decimal ariphmetic is exact.