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From 王旭 <wang...@sinosoft.com.cn>
Subject 答复: Some questions about the Derby
Date Fri, 21 Dec 2012 11:49:30 GMT
Hi  Knut

	Thank you for your reply , but I still have some problems need your help to answer.

	*Question one**:

	According to the reference manual:
	About divider,the scale expressions:  31 - lp + ls - rs
				the precision expressions: lp - ls + rp + max(ls + rp - rs + 1, 4)
	
	For example, the scale of the resulting data type of the following expression is 27:
    11.0/1111.33
	// 31 - 3 + 1 - 2 = 27
	Another, the precision of the resulting data type of the following expression is 14:
    11.0/1111.33
    //3 - 1 + 6 + Max(1+6-2+1,4) = 14

	Why the calculated results of the scale is less than the precision?
	I think that the precision (integer digits + scale digits) should be greater than the scale
digits.

	
	*Question two**:
	
	In ij, I re-verify these statements and the results the same with you.
	But I use java code using a JDBC connection Derby ,it will appear.
	Can you help me explain the problem?


-----邮件原件----
发件人: Knut Anders Hatlen [mailto:knut.hatlen@oracle.com] 
发送时间: 2012年12月20日 18:07
收件人: 王旭
抄送: derby-user@db.apache.org
主题: Re: Some questions about the Derby

Bryan Pendleton <bpendleton.derby@gmail.com> writes:

> Forwarding to the list.
> On 12/19/2012 04:10 AM, 王旭 wrote:

>> *Question one**:***
>> 
>> Firstly, I created a table.
>> 
>> CREATE TABLE CV
>> 
>>      (
>> 
>>          AGE INTEGER NOT NULL,
>> 
>>          RT DECIMAL(20,10),
>> 
>>          PRIMARY KEY (AGE)
>> 
>>      )
>> 
>> Then innserted data "insert into CV VALUES (80,10729.5000000000)"
>> 
>> Finally, an error occured when the SQL statement 
>> "select?(95000.0*1000/1000)/1000.0?*?RT?from?CV?where?Age=80?" was 
>> executed, it displayed  "the generated value has gone beyond the data 
>> type of DECIMAL / NUMERIC (31,25)".
>> 
>> Could you tell me how Derby do the precision control and operation on 
>> the data type of DECIMAL when it performs a variety of arithmetic 
>> operations including add, subtract, multiply and divide?

The reference manual explains how numeric types are promoted in expressions here: http://db.apache.org/derby/docs/10.9/ref/rrefsqlj27767.html

>> 
>> *Question two**:***
>> 
>> Firstly, I created a table.
>> 
>> CREATE TABLE CV
>> 
>>      (
>> 
>>          AGE SMALLINT,
>> 
>>          RT DOUBLE,
>> 
>>          PRIMARY KEY (AGE)
>> 
>>      )
>> 
>> Then innserted data "insert into CV VALUES (20,766.3)"
>> 
>> Finally, I got results of "268204.99999999994" after executing the 
>> SQL statement "select 350000.0/1000 * RT from CV the where age = 
>> 20?", but the actual result should be "268205.0".

When I execute those statements in ij, I see the result you expected:

ij> CREATE TABLE CV (AGE SMALLINT, RT DOUBLE, PRIMARY KEY (AGE));
0 rows inserted/updated/deleted
ij> insert into CV VALUES (20, 766.3);
1 row inserted/updated/deleted
ij> select 350000.0/1000 * RT from CV where age = 20;
1                     
----------------------
268205.0              

1 row selected

>> Could you tell me whether the cause of problem is inaccurated data 
>> from a floating-point type double.

That sounds likely. But it's difficult to tell without knowing exactly what you did when you
ended up with that number.


--
Knut Anders


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