Columns Returned by the GetSchemaTable Method
- Last Updated: April 16, 2026
- 4 minute read
- ADO.NET
- Documentation
While a DataReader is open, you can retrieve schema information from the result set. For each data provider, the result set produced for PrefixDataReader.GetSchemaTable() returns the columns described in the following table, in the order shown.
Columns Returned by GetSchemaTable on DataReader
| Column | Description |
| ColumnName | Specifies the name of the column, which might not be unique. If the name cannot be determined, a null value is returned. This name reflects the most recent renaming of the column in the current view or command text. |
| ColumnOrdinal | Specifies the ordinal of the column, which cannot be null. The bookmark column of the row, if any, is 0. Other columns are numbered starting with 1. |
| ColumnSize | Specifies the maximum possible length of a value in the column. For columns that use a fixed-length data type, this is the size of the data type. |
| NumericPrecision | If the ProviderType column is a numeric data type, this is the maximum precision of the column. If column type is not a numeric data type, the value is null. |
| NumericScale | If the column data type has a scale component, specifies the number of digits to the right of the decimal point. NumericScale applies to types with fractional seconds, such as Time and DateTime types. Otherwise, this is a null value. |
| DataType | The underlying type of the column. For the DB2 data provider, if Xml Describe Type is set to Binary, this should be a System.Byte[]. Otherwise, this should be System.String. Refer to the DataDirect Connect for ADO.NET User’s Guide for information about setting connection string options. This value cannot be null. |
| ProviderType | Specifies the provider-defined indicator of the column's data type. This column cannot be null. If the data type of the column varies from row to row, this must be Object. For the DB2 data provider, if Xml Describe Type is set to Binary, this should be a System.Byte[]. Otherwise, this should be System.String. |
| IsLong | Set if the column contains a BLOB, CLOB, LONG VARBINARY, LONG VARCHAR, or (for DB2) LONG VARGRAPHIC, that contains very long data. The definition of very long data is provider-specific. |
| AllowDBnull | Set to true if the AllowDbNull constraint is set to true for the column. Otherwise, the value is false. |
| IsReadOnly | The value is true if the column can be modified; otherwise, the value is false. |
| IsRowVersion | Is set if the column contains a persistent row identifier that cannot be written to, and has no meaningful value except to identify the row. |
| IsUnique | Specifies whether the column constitutes a key by itself or if there is a constraint of type UNIQUE that applies only to this column. When set to true, no two rows in the base table (the table returned in BaseTableName) can have the same value in this column. When set to false, the column can contain duplicate values in the base table. |
| IsKey | When set to true, the column is one of a set of columns that, taken together, uniquely identify the row in the DataTable. The set of columns with IsKey set to true must uniquely identify a row in the DataTable that may be generated from a DataTable primary key. When set to false, the column is not required to uniquely identify the row. |
| IsAutoIncrement | Specifies whether the column assigns values to new rows in fixed increments. When set to true, the column assigns values to new rows in fixed increments. When set to false, the column does not assign values to new rows in fixed increments. |
| BaseSchemaName | Specifies the name of the schema in the database that contains the column. The value is null if the base schema name cannot be determined. |
| BaseCatalogName | Specifies the name of the catalog in the data store that contains the column. A null value is used if the base catalog name cannot be determined. |
| BaseTableName | Specifies the name of the table or view in the data store that contains the column. A null value is used if the base table name cannot be determined. |
| BaseColumnName | Specifies the name of the column in the data store. This might be different than the column name returned in the ColumnName column if an alias was used. A null value is used if the base column name cannot be determined or if the rowset column is derived from, but is not identical to, a column in the database. |
| IsAliased | Specifies whether the name of the column is an alias. The value true is returned if the column name is an alias; otherwise, false is returned. |
| IsExpression | Specifies whether the name of the column is an expression. The value true is returned if the column is an expression; otherwise, false is returned. |
| IsIdentity | Specifies whether the name of the column is an identity column. The value true is returned if the column is an identity column; otherwise, false is returned. |
| IsHidden | Specifies whether the name of the column is hidden. The value true is returned if the column is hidden; otherwise, false is returned. |