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.
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: