Schema Collections

The Schema collections return metadata for the Advanced SQL Engine objects. The notable metadata columns for the Double data type are:

Column Name	Description
COLUMN_TYPE or DATA_TYPE	Set to DOUBLE PRECISION.
NUMERIC_PRECISION	Set to 15.
FORMAT	Format assigned to the SQL Engine object.
PROVIDERDBTYPE	It is set to TdType.Double.

Schema Table

The TdDataReader.GetSchemaTable returns result set metadata. The notable metadata columns for the Double data type are:

Column Name

Description

NumericPrecision

Set to 15.

DataType

System.Type object for the System.Double type.

ProviderType

Set to TdType.Double.

Format

Format assigned to the SQL Engine object.

ProviderSpecificDataType

System.Type object for the System.Double structure.

Note
The Data Provider does not have a Provider Specific Type corresponding to the SQL Engine Double data type. The Data Provider returns System.Double data type from the Provider Specific Value methods.

Configuring Parameters

The following example shows how to configure a Double parameter using DbType type declaration and a BCL value.

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TdParameter quantity = new TdParameter(); quantity.DbType = DbType.Double; quantity.Value = 1.2349;

The following example shows how to configure a Double parameter using TdType type declaration and a BCL value.

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TdParameter quantity= new TdParameter(); quantity.TdType = TdType.Double; quantity.Value = Double.Epsilon;

Note
The SQL Engine DOUBLE PRECISION data type officially supports ±2.226 x 10^-308 to ±1.797 x 10³⁰⁸ range of values.

Specifying Double as Literal

The syntax for the Double Precision Literal is ±n.nE±m. Double literal consist of an optional sign, up to 15 digits representing the whole and fractional components of the mantissa, literal character E, optional sign and finally up to 3 digits representing the exponent.

Note
We recommend to always use Parameters in order to take advantage of the SQL Engine's Request Cache.

The following example shows 12,987,561 represented as Double Literal in the Command Text.

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using (TdConnection cn = new TdConnection("data source=x;UserId=y;Password=z;")) { cn.Open(); TdCommand cmd = cn.CreateCommand(); cmd.CommandText = "SELECT Id, orderDate from Order where quantity > 1.2987561E7 "; using (TdDataReader reader = cmd.ExecuteReader()) { if (reader.HasRows) { while (reader.Read()) { Console.WriteLine("Id={0}, orderDate={1}", reader.GetInt64(0), reader.GetDate(1)); } } } }

Copy Code

using (TdConnection cn = new TdConnection("data source=x;UserId=y;Password=z;"))
{
    cn.Open();
    TdCommand cmd = cn.CreateCommand();

    cmd.CommandText = "SELECT Id, orderDate from Order where quantity > 1.2987561E7  ";

    using (TdDataReader reader = cmd.ExecuteReader())
    {
        if (reader.HasRows)
        {
            while (reader.Read())
            {
                Console.WriteLine("Id={0}, orderDate={1}", reader.GetInt64(0), reader.GetDate(1));
            }
        }
    }
}

Retrieving Double Data

The following methods and properties return the column or parameter value as a System.Double structure.

The following Provider Specific Value method and property return the column or parameter value as a System.Double structure.

Note
The Data Provider does not have a Provider Specific Type corresponding to the Double Precision data type. The Data Provider returns System.Double data type from the Provider Specific Value methods.

C#	Copy Code
using (TdConnection cn = new TdConnection("data source=DS1;UserId=Joe;Password=XY;")) { cn.Open(); TdCommand cmd = cn.CreateCommand(); cmd.CommandText = "SELECT Id, Quantity from Order where Quantity > ?"; cmd.Parameters.Add("quantity", TdType.Double); cmd.Parameters["quantity"].Value = 1.2987561E+7; using (TdDataReader reader = cmd.ExecuteReader()) { if (reader.HasRows) { while (reader.Read()) { Console.WriteLine("[System.Double] Quantity = {0}", reader.GetDouble(1).ToString()); } } } } /* Output: [System.Double] Quantity = 1.3E+7; */