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?