I have an SSIS ETL process in which i use the multiple flat file connection to create 2 main tables:
I then have a cursor to union these 2 tables in SELECT Statement. In the SELECT statement i am selecting most (almost all) of the columns. This cursor populates other normalized tables, so the source tables are essentially read only after the ETL process is done.
My question is:
How can i improve the performance of this SELECT? The union of the 2 tables produces about 3m rows and takes about 15 mins
There are no indexes on each of the source tables in the union.