Check out example codes for "c# merge two lists as queryable". It will help you in understanding the concepts better.

Code Example 1

var list3 = list1.Concat(list2);

// or

var list4 = list1.Union(list2);
// Union is a set operation - it returns distinct values.

// Concat simply returns the items from the first sequence followed by the items from the second sequence; the resulting sequence can include duplicate items.

// You can think of Union as Concat followed by Distinct.

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