I am working in BIRT and do some report. In this report, there is a table,
which connects one data to another (has 2 columns). For example, item "a"
connected to item "b", then item "b" connected to item "c". Next item "y"
may be connected to item "b" too. Max level of connection is 10. So, i
made a select statement, using LEFT JOIN. It gets all items (even if they
do not connected) and get their connection, if they exists (if they do not
exist, there is null, but this is ok - there is a hide condition on this
rows - so you don't see them). But there is a problem - there is some
number, that is connected to each item. If a level exists, then number is
retrieved from database also, and all is OK. But if a level didn't exists,
then there is a null in the field with 'DOUBLE' data type.
When i call 'Preview Data Set' then strings with 'null' value is simply
"empty" and all is ok. But DOUBLES with 'null' value produce an error
message : "The data type is double, but value is null - it can't be
converted to double". Why the string look like empty when it is null, and
double doesn't? How can i put the 0.0 (for example) in double if it is
null? I can't even preview data set.