Teradata 中的 DECIMAL 类型 [英] DECIMAL Types in Teradata

问题描述

谁能解释一下我在 Teradata 中得到的以下结果:

Can somebody please explain the following result I get in Teradata:

SELECT TYPE(CAST (2.3 AS DECIMAL(18,4)) * CAST (2.3 AS DECIMAL(18,4))  )

结果是:

DECIMAL(18,8)

我期待 DECIMAL(18,4)

I was expecting DECIMAL(18,4)

推荐答案

对于涉及小数的计算，每个 DBMS 都有自己的规则.

Every DBMS has it's own rules regarding calculations involving Decimals.

Teradata 的基本规则是:当您添加/减去/除以 DECIMAL 时，得到的小数精度是两个操作数中较大的一个，例如dec(10,2) + dec(10,4) = dec(xx,4)

Teradata's basic rules are: When you add/substract/divide DECIMALs the resulting fractional precision is the greater of both operands, e.g. dec(10,2) + dec(10,4) = dec(xx,4)

但是当你乘以小数位数时，例如dec(10,2) * dec(10,4) = dec(xx,6)

But when you multiply the fractional digits are added, e.g.dec(10,2) * dec(10,4) = dec(xx,6)

整体精度有更多规则(一些取决于 dbscontrol MAxDecimal 设置).

The overall precision has some more rules (some depending on the dbscontrol MAxDecimal setting).

然后是最重要的规则，人们往往会忘记:每次计算后，结果都会四舍五入到这个精度.

And then there's the most important rule, people tend to forget: After each calculation the result is rounded to this precision.

sel 2.0/3.00 * 100, 100*2.0/3.00;

    *** Query completed. One row found. 2 columns returned.
    *** Total elapsed time was 1 second.

 ((2.0/3.00)*100)   ((100*2.0)/3.00)
-----------------  -----------------
            67.00              66.67

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