Modification of Tables

Elements in a table can be inserted, changed, and deleted. These functions are all performed by the WRITE/TABLE or COPY commands (See Table 5.4). The element to be modified must be defined by giving its column and row location. An element is deleted if the value is set to NULL. A whole row is considered deleted if the element in the reference column is NULL. The data type of a column cannot be changed once the column has been created. However, the command COPY/TT can be used to copy and convert the values of a column of a certain type into a column of an another type.

  
Table: Commands to Modify a Table

It is possible to define a ``subset'' of a table by the SELECT command. All commands that do not change a table element will only use the subset selected. By selecting ALL the whole table is selected.

It is also possible to transfer data from one table to another. The four commands described in Table can be used.

  
Table: Commands to Transfer Table Data

Interactive identification of table entries is done with the command IDENTIFY/xxx, where xxx is CURSOR for the image display and GCURSOR for the graphic screen.