Wavetronix Command Translator (CMD-DT) - User Guide - Manual (Page 125)

124 CHAPTER 11 • TASKBUILDER SUB-WINDOWS
˽ Select the desired source column then drag the cursor from the source column to the
desired destination column. A blue guideline will appear to show the mapping line as
it goes across the screen.
Below is a list of rules concerning column mappings:
˽ Multiple Source Columns to Destination Columns – Multiple source columns may
NOT map to the same destination column. If a destination column already has a map-
ping associated with it, attempting to create another one will result in an error. You can,
however, map one source column to two or more different destination columns.
˽ Type Compatibility – TaskBuilder will automatically check for type compatibility and
will show an error message if two types are incompatible. Conversions exist between
many different data types; columns do not have to be the same type to be compatible.
Any Source column can be mapped to a String column. Number columns can be con-
verted to other number columns, but there may be some data loss. A sub-window will
inform you when there is a possibility of data loss or when a conversion is not allowed.
˽ Data Loss – It is possible to map larger columns into smaller ones (i.e. a 32-bit number
into a 16-bit number, or a floating point decimal number into an integer). However,
this creates the possibility of data loss because the number is truncated to fit into a
smaller space. When this type of mapping is formed, TaskBuilder will create the map-
ping but will also show a message box warning of the potential for data loss. Text col-
umns within databases will commonly have fixed-length designations which deter-
mine a max length for the text value. Copying text from a source column with a longer
text field to a destination column with a shorter text field can also lead to data loss
when the task is run and the source text is truncated.
˽ Unsafe Mappings – Some mappings are considered valid from a TaskBuilder perspec-
tive but may lead to errors at run-time when the task is executed. A mapping of a text
string column to a numerical column, for example, requires that all the text strings in
the source column be in numerical form that can be converted directly to numbers.
Any non-numeric text strings in the source table will cause the task to fail when run.
Default Values
A complete mapping requires values for each column in the destination table. A default
value will need to be provided when destination columns do not have a mapping to any
source column. This default value will be inserted into the column for each data row copied
over from the source database. TaskBuilder does not currently support mapping columns
from two or more different source tables into one destination table. For these transforma-
tions, a DB-to-Data-to-DB task will need to be created (see Appendix A).