# Table Compare Column Settings Session > Session Settings > Columns |

Each line in the display represents a comparison column, and shows: •Comparison if key, column number, column name •Left file column number, sample data if available •Right file column number, sample data if available •Handling summary of column comparison To control the alignment of rows Define as many columns as keys as necessary to uniquely identify each row. By default, the first column is the only one defined as a key. To define a column as a key, position on the appropriate line, click the Edit button, mark the Key checkbox, and click OK. If multiple keys are defined, precedence follows the order in the comparison. If no keys are defined, the alignment will use all of the columns to uniquely identify each row. To control the alignment of columns By default, the comparison assumes the columns of the files are in the same order. To change the comparison order of a column in the left file, position on the appropriate line under Left file, and click the Move Up or Move Down button as necessary. If you position under Comparison instead, those buttons will change the position of the comparison column itself. To prevent a column in the left file from being compared at all, position on the appropriate line under Left file, and click the Remove button. If you position under Comparison instead, this button will prevent its file columns from being compared and delete this comparison column definition. To restore a removed column from the left file, position under Left file, click the Insert button, mark items in the Insert Columns dialog and click OK. Click the Tidy button to remove any blank lines from the list. To control the names of columns By default, column names are automatically determined from the left or right file. To give a column a specific name, position on the appropriate line, click the Edit button, change the Name, and click OK. To revert all columns to automatic naming, pick Reset Names from the list's right-click menu. If left file data is available, you can pick Fill Names Using Left File from the list's right-click menu to force the names to be those found in the left file. Fill Names Using Comparison will force the names to be those that would be automatically determined. To control how column data is compared Position on the appropriate line and click the Edit button to open the Column Handling dialog. To change the default Handling settings, click the Edit Default button.