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Fix for bug #43432: Union on floats does unnecessary rounding

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UNION could convert fixed-point FLOAT(M,D)/DOUBLE(M,D) columns  
to FLOAT/DOUBLE when aggregating data types from the SELECT  
substatements. While there is nothing particularly wrong with  
this behavior, especially when M is greater than the hardware  
precision limits, it could be confusing in cases when all  
SELECT statements in a union have the same  
FLOAT(M,D)/DOUBLE(M,D) columns with equal precision  
specifications listed in the same position.  
  
Since the manual is quite vague on what data type should be  
returned in such cases, the bug was fixed by implementing the  
most 'expected' behavior: do not convert FLOAT(M,D)/DOUBLE(M,D)  
to anything else if all SELECT statements in a UNION have the  
same precision for that column.
This commit is contained in:
Alexey Kopytov
2009-03-27 13:12:50 +03:00
parent 8725bcd944
commit afb2b6de68
5 changed files with 54 additions and 14 deletions
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12
mysql-test/r/union.result
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@ -1506,4 +1506,16 @@ DESC t6;
Field Type Null Key Default Extra
NULL int(11) YES NULL
DROP TABLE t1, t2, t3, t4, t5, t6;
CREATE TABLE t1 (f FLOAT(9,6));
CREATE TABLE t2 AS SELECT f FROM t1 UNION SELECT f FROM t1;
SHOW FIELDS FROM t2;
Field Type Null Key Default Extra
f float(9,6) YES NULL
DROP TABLE t1, t2;
CREATE TABLE t1(d DOUBLE(9,6));
CREATE TABLE t2 AS SELECT d FROM t1 UNION SELECT d FROM t1;
SHOW FIELDS FROM t2;
Field Type Null Key Default Extra
d double(9,6) YES NULL
DROP TABLE t1, t2;
End of 5.0 tests