SQL 服务器 INFORMATION_SCHEMA 报告的浮点精度与 ADO.NET GetSchemaTable() 不同？

Question

对于声明为 float 的 SQL 服务器列，INFORMATION_SCHEMA 报告数值精度为 53，而 ADO.NET SqlDataReader.GetSchemaTable() 方法报告 15 . 造成这种明显差异的原因是什么？

这是 VB 中的一个最小代码示例：

Private Sub MinimalCodeExample(conn As DbConnection)
  Try
    CreateTestTable(conn)
    Dim precisionFromInformationSchema As Integer =
      GetPrecisionFromInformationSchema(conn) ' 53
    Dim precisionFromADONETSchemaTable As Integer =
      GetPrecisionFromADONETSchemaTable(conn) ' 15

    ' Why does this assertion fail, 53 <> 15?
    Debug.Assert(precisionFromInformationSchema = precisionFromADONETSchemaTable)
  Finally
    CleanUpTestTable(conn)
  End Try
End Sub

Private Sub CreateTestTable(conn As DbConnection)
  Dim cmd As DbCommand = conn.CreateCommand()
  cmd.CommandText = "CREATE TABLE WhosebugEXAMPLE(value float)"
  cmd.ExecuteNonQuery()
End Sub

Private Function GetPrecisionFromInformationSchema(conn As DbConnection) As Integer
  Using cmd As DbCommand = conn.CreateCommand()
    cmd.CommandText = "SELECT NUMERIC_PRECISION FROM INFORMATION_SCHEMA.COLUMNS WHERE TABLE_NAME='WhosebugEXAMPLE'"
    Return CInt(cmd.ExecuteScalar())
  End Using
End Function

Private Function GetPrecisionFromADONETSchemaTable(conn As DbConnection) As Integer
  Using cmd As DbCommand = conn.CreateCommand()
    cmd.CommandText = "SELECT value FROM WhosebugEXAMPLE"
    Using reader As DbDataReader = cmd.ExecuteReader(CommandBehavior.SchemaOnly Or CommandBehavior.KeyInfo)
      Using dt As DataTable = reader.GetSchemaTable()
        Return CInt(dt.Select("ColumnName='value'").Single()("NumericPrecision"))
      End Using
    End Using
  End Using
End Function

Private Sub CleanUpTestTable(conn As DbConnection)
  Using cmd As DbCommand = conn.CreateCommand()
    cmd.CommandText = "DROP TABLE WhosebugEXAMPLE"
    cmd.ExecuteNonQuery()
  End Using
End Sub

Answer 1

基本上，53个在bits，15个在digits。

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.

float and real (TSQL)

并且在 ADO.NET 中，所有数字数据类型的 "NumericPrecision" 表示该数据类型可以存储的小数位数。

SQL 服务器 INFORMATION_SCHEMA 报告的浮点精度与 ADO.NET GetSchemaTable() 不同？

SQL Server INFORMATION_SCHEMA reports different float precision than ADO.NET GetSchemaTable()?

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