SET QUOTED_IDENTIFIER (Transact-SQL)

Causes SQL Server to follow the ISO rules for quotation-delimited identifiers and literal strings. identifiers delimited by double quotation marks can be Transact-SQL reserved keywords, or they can contain characters that are normally disallowed by the Transact-SQL identifier syntax conventions.

When SET QUOTED_IDENTIFIER is on, identifiers can be delimited by double quotation marks, and literals must be separated by single quotation marks.When SET QUOTED_IDENTIFIER is OFF, identifiers are not quoted and must conform to all Transact-SQL identifier rules. For more information, see database identifiers. text can be delimited by single or double quotation marks.

When SET QUOTED_IDENTIFIER is on (the default value), all strings separated by double quotation marks are interpreted as object identifiers.Therefore, the quoted identifiers do not have to conform to the Transact-SQL identifier rules.They can be reserved keywords and can contain characters that are not normally allowed in Transact-SQL identifiers. You cannot use double quotation marks to separate literal string expressions, but you must enclose literal strings in single quotation marks.   If the single quotation mark ( ' ) is part of a literal string, it can be represented by two single quotation marks ( ").  

When SET QUOTED_IDENTIFIER is OFF, the literal strings in the expression can be separated by either single or double quotation marks. if the literal string is delimited by double quotation marks, you can include embedded single quotation marks, such as ellipses, in the string.

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SET QUOTED_IDENTIFIER (Transact-SQL)