LINQ to Objects extends any type that inherits from IEnumerable (which is almost every collection class in .NET, from simple Arrays to List<T>) to support query operations similar to those available in SQL. We can write queries using any of the built-in Standard Query Operators, or add our own operators if we need to. The standard operators cover a wide variety of categories, at present there are over fifty that form the backbone of LINQ. To get an idea of their scope, here is a list of those operators available to us –
| Operator Type | Operator Name |
| Aggregation | Aggregate, Average, Count, LongCount, Max, Min, Sum |
| Conversion | Cast, OfType, ToArray, ToDictionary, ToList, ToLookup, ToSequence |
| Element | DefaultIfEmpty, ElementAt, ElementAtOrDefault, First, FirstOrDefault, Last, LastOrDefault, Single, SingleOrDefault |
| Equality | EqualAll |
| Generation | Empty, Range, Repeat |
| Grouping | GroupBy |
| Joining | GroupJoin, Join |
| Ordering | OrderBy, ThenBy, OrderByDescending, ThenByDescending, Reverse |
| Partitioning | Skip, SkipWhile, Take, TakeWhile |
| Quantifiers | All, Any, Contains |
| Restriction | Where |
| Selection | Select, SelectMany |
| Set | Concat, Distinct, Except, Intersect, Union |
Most of the operators should be familiar if you have ever worked with a relational database writing queries in SQL.
One important distinction between writing SQL queries and LINQ queries is that the operator order is reversed. If you are used to Select-From-Where-OrderBy, it might take some time to overcome the muscle memory and move to From-Where-OrderBy-Select.
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