Web System Manage fields

The first tab - Columns allows you to Add (New), Edit, or Delete (Drop) Columns.The Button 'New'  opens a dialog box for the Column attributes input.  The Button [Edit]  opens a dialog box for editing field properties. ► Also, this dialog can be accessed by double-clicking a field in the list.  Note the image below does not have any columns yet.

Name — Name of the column. The name of the column must be unique for this Table. You cannot create a table with two fields named the same. The name of the field must be in lower case Latin alphabet only. Only underscore is accepted as an additional symbol  ( _ ). 
Type — The type of data saved in the field. For example, NUMERIC type is appropriate for salary data.
Length — Controls the length of the line for CHARACTER VARYING type fields or the number of decimal places in NUMERIC type fields.
Precision — Number of digits after the decimal separator for NUMERIC type fields.
Default — Sets a default value for data if no data is entered.  Similar to 'autoentering a value'.
Not Null — Prohibits nulls.
Description — A description of the column. A line of text that does not affect the performance of the database and is there for the convenience of a user.

The Button [Drop] — Deletes a Column from the table.  Ideally, you should decide on your Table Structure and column datatypes before inserting too much data.

Delete a column from a table and the data in this column is deleted and cannot be recovered.

Hint: It's a good idea is to create a sample Table with one column assigned to each datatype.  Enter data and view your results. A few generalizations - that are often true: Allowing Null values in a Table can lead to unexpected Query results and be a general nuisance.  Use Numeric for money Use Character varying or Text if any non-numeric charcters are to be entered.  Example is a phone number formatted as '555-1212'.  As displayed, it is not truly, a number. Write a good description.  Other users may need it - and if you forget, you'll have a reminder of what it means. Avoid extremely long Names Note that we use the words 'Column' and 'Field' interchangeably.  'Column' is more correct - but 'Field' may be more recognizeable by users of Applications such as Filemaker™, etc.