This week’s installment in the series on efficient data is all about data types. Be smart about choosing them; The right type for the right job will not only store your data in less physical space and enforce data integrity better, but smaller indexes and tables will also improve overall query performance.
update in place
The assert operator and different types of updates
When you update a column that is tied to a foreign key constraint, SQL Server needs to validate (called “assert“) the new value, in order to make sure that you haven’t added a value with no matching primary key. But in some situations, it’ll assert more than just the column(s) you updated.
sqlsunday.com 