Dualcore DBA takes a look at a historical problem:
The Halloween Problem gets its name from the day it was discovered – 31st October (some reports differ between 1975 and 1976). On this day, Donald Chamberlin, Patricia Selinger, and Morton M. Astrahan were working on the System R database project in an IBM lab and wrote a SQL query which updated a database, giving each staff member who earned less than $25,000 a 10% pay rise. The query completed, but every staff member then had a salary of at least $25,000 – this was not the expected output of the query.
They had inadvertently found a flaw in how the update was being executed – some affected records were updated more than once, until they no longer matched the filter criteria.
Click through to see how most data platforms, including SQL Server, resolve this issue.