Doug's reply tells you the best way to approach what you are doing if all
the data you need is related (e.g. to a myrecordID field somewhere), but if
necesary you may be able to get information from various data sources into a
document using { DATABASE } fields.
Typically in the context of a merge you need to nest a { MERGEFIELD
myrecordID } field in a WHERE clause int he SQL in the { DATABASE } field if
you need to retrieve data related to the current record being merged. To
ensure the result is just text, not a table, retrieve one column and do not
use the \h switch in the field.