LINQ: When to use SingleOrDefault vs. FirstOrDefault() with filtering criteria

Question

Consider the IEnumerable extension methods SingleOrDefault() and FirstOrDefault()

MSDN documents that SingleOrDefault:

Answer 1

For LINQ -> SQL:

SingleOrDefault

• will generate query like "select * from users where userid = 1"
• Select matching record, Throws exception if more than one records found
• Use if you are fetching data based on primary/unique key column

FirstOrDefault

• will generate query like "select top 1 * from users where userid = 1"
• Select first matching rows
• Use if you are fetching data based on non primary/unique key column