C# Language Specification

Ambiguities in query expressions

Query expressions contain a number of “contextual keywords”, i.e., identifiers that have special meaning in a given context. Specifically these are from, where, join, on, equals, into, let, orderby, ascending, descending, select, group and by. In order to avoid ambiguities in query expressions caused by mixed use of these identifiers as keywords or simple names, these identifiers are considered keywords when occurring anywhere within a query expression.

For this purpose, a query expression is any expression that starts with “from identifier” followed by any token except “;”, “=” or “,”.

In order to use these words as identifiers within a query expression, they can be prefixed with “@” (§2.4.2).

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