sql - oracle中<number>d或<number>f是什么意思？

Question

下面是从对偶表中选择100的正常执行:

SQL> select 100 from dual;

       100
----------
       100

这是将 'a' 添加到数字 100 的相同执行，它只是设置列名称。对于除 d 和 f 之外的任何其他字母表，结果都是相同的。

SQL> select 100a from dual;

         A
----------
       100

这是将 'd' 和 'f' 添加到数字 100

的相同执行

SQL> select 100d from dual;

      100D
----------
  1.0E+002

SQL> select 100f from dual;

      100F
----------
  1.0E+002

它有什么用？什么意思？

Answer 1

d 和 f 用于隐式声明数字为 float 。

1.0E+002 是 scientific notation 100

100a 只是被 oracle 解释为数字值 100 别名 a。

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官方文档NUMBER and Floating-Point Literals

f or F indicates that the number is a 32-bit binary floating point number (of type BINARY_FLOAT).

d or D indicates that the number is a 64-bit binary floating point number (of type BINARY_DOUBLE)

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可以在 ROUND() function 中找到此行为的示例文档

The following examples illustrate the difference between rounding NUMBER and floating-point number values. NUMBER values are rounded up (for positive values), whereas floating-point numbers are rounded toward the nearest even value:

SELECT ROUND(1.5), ROUND(2.5) FROM DUAL;

ROUND(1.5) ROUND(2.5)
---------- ----------
         2          3

SELECT ROUND(1.5f), ROUND(2.5f) FROM DUAL;

ROUND(1.5F) ROUND(2.5F)
----------- -----------
   2.0E+000    2.0E+000