在数据库 Sql 服务器中存储为 Real 的浮点数

Question

为什么 Float 在 sys.columns 中存储为 Real 或在 precision <= 24 中存储为 Information_schema.columns。

CREATE TABLE dummy
  (
     a FLOAT(24),
     b FLOAT(25)
  )

检查数据类型

SELECT TABLE_NAME,
       COLUMN_NAME,
       DATA_TYPE,
       NUMERIC_PRECISION
FROM   INFORMATION_SCHEMA.COLUMNS
WHERE  TABLE_NAME = 'dummy'

结果：

+------------+-------------+-----------+-------------------+
| TABLE_NAME | COLUMN_NAME | DATA_TYPE | NUMERIC_PRECISION |
+------------+-------------+-----------+-------------------+
| dummy      | a           | real      |                24 |
| dummy      | b           | float     |                53 |
+------------+-------------+-----------+-------------------+

那么当precision小于或等于24时，为什么float存储为real。这在某处记录了吗？

Answer 1

The ISO synonym for real is float(24).

Please refer for more info:
https://msdn.microsoft.com/en-us/library/ms173773.aspx

Answer 2

来自讨论 T-SQL 中 float 和 real 之间区别的 MSDN article：

The ISO synonym for real is float(24).

float [ (n) ]

Where n is the number of bits that are used to store the mantissa of the float number in scientific notation and, therefore, dictates the precision and storage size. If n is specified, it must be a value between 1 and 53. The default value of n is 53.

n value | Precision | Storage size
1-24    | 7 digits  | 4 bytes
24-53   | 15 digits | 8 bytes

SQL Server treats n as one of two possible values. If 1<=n<=24, n is treated as 24. If 25<=n<=53, n is treated as 53.

至于为什么SQL服务器将其标记为real，我认为它只是一个同义词。但是，在引擎盖下它仍然是 float(24).

在数据库 Sql 服务器中存储为 Real 的浮点数

Float stored as Real in database Sql Server

sql

tsql

sql-server

precision

sqldatatypes