SQL query returns value but EXEC SQL Task fails to assign variable

Question

I have an execute SQL task to get an identifier from an Oracle database and assign it to a variable (the variable is used in subsequent query's where clauses to transfer the data to a SQL Server database). If I copy the query from the SSIS
package to the Oracle SQL Developer interface and run the query; I get the expected single identifier. If I run the execute SQL task I get the error "[Execute SQL Task] Error: An error occurred while assigning a value to variable "VariableName":
"Single Row result set is specified, but no rows were returned."
I can create phony/simpler versions of the query that will return the wrong identifier that will successfully assign the value to the variable, so the problem isn't with the variable itself or the way the result set is set up in the task (Result
Set/Single Row in the General panel; Result Name 0/VariableName in the Result Set panel).
How can two queries that return a single value produce different results with respect to the variable assignment process?

Answer 1

Perhaps you can trap (profile) the query in Oracle to see what it gets submitted,
thing is this query
select id from table where ProcessedStatusColumn is null and DateColumn = (sub select to get most recent date in table where ProcessedStatusColumn is null)
is not guaranteed to return a value, you need a default returned in case the search failed e.g.
select
NVL(id, 0)
from table where ProcessedStatusColumn is null and DateColumn =
(sub select to get most recent date in table where
ProcessedStatusColumn is null)
Arthur My Blog