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Microsoft SQL identifiers
The rules for the format of regular identifiers depend on the database compatibility level. Usually the following rules apply:
1. The first character must be one of the following:
| • | A letter as defined by the Unicode Standard 3.2. The Unicode definition of letters includes Latin characters from a through z, from A through Z, and also letter characters from other languages. |
| • | The underscore (_), "at" sign (@), or number sign (#). |
| • | Certain symbols at the beginning of an identifier have special meaning in SQL Server. An identifier that starts with the "at" sign denotes a local variable or parameter. An identifier that starts with a number sign denotes a temporary table or procedure. An identifier that starts with double number signs (##) denotes a global temporary object. |
| • | Some Transact-SQL functions have names that start with double at signs (@@). To avoid confusion with these functions, you should not use names that start with @@. |
2. Subsequent characters can include the following:
| • | Letters as defined in the Unicode Standard 3.2. |
| • | Decimal numbers from either Basic Latin or other national scripts. |
| • | The "at" sign, dollar sign ($), number sign, or underscore. |
3. The identifier must not be a Transact-SQL reserved word. SQL Server reserves both the uppercase and lowercase versions of reserved words.
4. Embedded spaces or special characters are not allowed.
When they are used in Transact-SQL statements, identifiers that do not comply with these rules must be delimited by double quotation marks or brackets.
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