Name

GetSchemaTable

Synopsis

DataTable dt = DataReader.GetSchemaTable();

Returns a DataTable that contains metadata for the current query. This table contains one row for each column in the result set and several fields that describe details such as column names and data types. Table 21-2 lists all columns returned in the schema DataTable, in order.

Table 21-2. Schema columns

Column	Description
ColumnName	The name of the column. If the query renamed the column using the AS keyword, this is the new name.
ColumnOrdinal	The ordinal number of the column.
ColumnSize	The maximum allowed length of values in the column or the size of the data type for fixed-length data type.
NumericPrecision	The maximum precision (number of digits) of the column for a numeric data type or null for all other data types.
NumericScale	The maximum scale (number of digits to the right of the decimal point) of the column for a numeric data type, or null for all other data types.
IsUnique	Indicates whether or not column values can be duplicated.
IsKey	Indicates whether or not this column is part of the primary key for the table.
BaseCatalogName	The name of the database that contains this table, or null if it can’t be determined.
BaseColumnName	The name of the column in the data source. If the query renamed the column using the AS keyword, this is the original name.
BaseSchemaName	The name of the schema in the data source, or null if it can’t be determined.
BaseTableName	The name of the table or view in the data source that contains this column, or null if it can’t be determined.
DataType	The mapped .NET framework type.
AllowDBNull	Indicates whether null values are accepted for column values.
ProviderType	Indicates the provider-specific data type.
IsAliased	True if the column has been renamed using the AS keyword.
IsExpression	True if the column is calculated based on an expression.
IsIdentity	True if the column is an identity value generated by the data source.
IsAutoIncrement	True if column values are assigned by the data source in fixed increments.
IsRowVersion	True if the column contains a read-only row identifier.
IsHidden	True if the column is hidden.
IsLong	True if the column contains a binary long object (BLOB).
IsReadOnly	True if the column can’t be modified.

Example

The following example retrieves a schema table and displays the returned information. The schema information describes the columns from the Customers table.

SqlCommand cmd = new SqlCommand("SELECT * FROM CUSTOMERS", con);



// Get the schema table.

con.Open();

SqlDataReader r = cmd.ExecuteReader();

DataTable schema = r.GetSchemaTable();

con.Close();



// Display schema table information.

foreach (DataRow row in schema.Rows)

{

    foreach (DataColumn col in schema.Columns)

    {

        Console.WriteLine(col.ColumnName + " = " + row[col].ToString());

    }

    Console.WriteLine();

}