[ http://issues.apache.org/jira/browse/DERBY-1139?page=all ]
Rick Hillegas updated DERBY-1139:
---------------------------------
Priority: Major (was: Critical)
Downgrading the priority of this issue to Major since according to Satheesh's
analysis, Derby behavior seems to be correct albeit confusing. A warning or
extra documentation could help clear up the confusion.
> Division operator may give wrong results with NUMERIC operands
> --------------------------------------------------------------
>
> Key: DERBY-1139
> URL: http://issues.apache.org/jira/browse/DERBY-1139
> Project: Derby
> Type: Bug
> Components: SQL
> Versions: 10.1.2.1
> Reporter: Matthias Ohlemeyer
>
> The division operator '/' may give wrong results when used with NUMRERIC
> operands.
> Example (copied from ij):
> CREATE TABLE t (d1 DOUBLE, d2 DOUBLE, n1 NUMERIC(31,11), n2
> NUMERIC(31,11));
> INSERT INTO t VALUES (1.5, 2.5, 1.5, 2.5);
> SELECT d1/d2, n1/n2, n1*(1.0/n2) FROM t;
> 1 |2 |3
> ----------------------------------------------------------------
> 0.6 |0 |0.600000000000000000000000000000
> 1 row selected
> The result in column 2 should not be zero, but 0.6.
> It seems there is something wrong with the calculation of the scale. Hint
> from Satheesh Bandaram:
> If you look at NumericTypeCompiler code, which calculates the scale and
> precision of operation result type, the comments and the code doesn't seem to
> match. (getScale() method):
> NumericTypeCompiler.java
> else if (TypeCompiler.DIVIDE_OP.equals(operator))
> {
> /*
> ** Take max left scale + right precision - right scale + 1,
> ** or 4, whichever is biggest
> */
> LanguageConnectionContext lcc = (LanguageConnectionContext)
>
> (ContextService.getContext(LanguageConnectionContext.CONTEXT_ID));
> // Scale: 31 - left precision + left scale - right scale
> val = Math.max(NumberDataValue.MAX_DECIMAL_PRECISION_SCALE -
> lprec + lscale - rscale, 0);
> }
> Here val is returning zero for scale, it seems.
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