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 5.4: Commands to Modify a Table

Command	Description
WRITE/TABLE	Write value into a table element.
COPY/KT	Copy a keyword into a table element.
COPY/TK	Copy a table element into a keyword.
COPY/TT	Copy columns values into another column.
COPY/TI	Transform the format of the file from table into image.
COPY/IT	Transform the format of the file from image into 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 5.5 can be used.

 

Table 5.5: Commands to Transfer Table Data

Command	Description
COPY/TT	Copy all selected elements with identical reference values.
COPY/TABLE	Copy all selected elements from one table into another.
MERGE/TABLE	Merge common columns in several tables.
PROJECT/TABLE	Copy a set of columns from one table into another.

 

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.