joinondifferentdatatype-创新互联

SELECT ....
FROM A LEFT SEMI JOIN B
ON (A.col1 = B.col2)
WHERE ...
"
If A.col1 is of DOUBLE type, but B.col2 is of BIGINT,  will print WARNING: Comparing a bigint and a double may result in a loss of precision.  Why can't cast col2 to double automatically?

站在用户的角度思考问题，与客户深入沟通，找到津市网站设计与津市网站推广的解决方案，凭借多年的经验，让设计与互联网技术结合，创造个性化、用户体验好的作品，建站类型包括：成都网站设计、网站建设、企业官网、英文网站、手机端网站、网站推广、国际域名空间、虚拟空间、企业邮箱。业务覆盖津市地区。

> If A.col1 is of DOUBLE type,

> but B.col2 is of BIGINT,

The automatic conversion is not acceptable according to the java language

spec (section 5.1.2)

https://docs.oracle.com/javase/specs/jls/se7/html/jls-5.html#jls-5.1.2

Also to be noted here is that in general, that even if you cast, you might

be casting the wrong way around.

Because joins on double columns will give incorrect (rather unintended,

but IEEE 754 correct) results when comparing byte serialized

representations - because of the nearly-equal property epsilon.

Easiest way to demonstrate this is to try the simplest off-by-epsilon case

(say, in python)

>>> import sys

>>> 0.1 + 0.2

0.30000000000000004

>>> 0.1 + 0.2 > 0.3

True

>>>

>>> ((0.1+0.2) - 0.3) < sys.float_info.epsilon

True

So if the RHS produced ETL values by sum() and the LHS was produced by

parsing log text, the JOIN will output zero rows.

If you want to do equijoins like that, the only valid case is to cast both

to fixed precision bigints (say, convert all dollars to cents, by *100),

not both to double.

Cheers,

Gopal

另外有需要云服务器可以了解下创新互联scvps.cn，海内外云服务器15元起步，三天无理由+7*72小时售后在线，公司持有idc许可证，提供“云服务器、裸金属服务器、高防服务器、香港服务器、美国服务器、虚拟主机、免备案服务器”等云主机租用服务以及企业上云的综合解决方案，具有“安全稳定、简单易用、服务可用性高、性价比高”等特点与优势，专为企业上云打造定制，能够满足用户丰富、多元化的应用场景需求。

本文名称：joinondifferentdatatype-创新互联
文章链接：http://6mz.cn/article/gjgpd.html