Why Use Square Brackets in MS-SQL Column Names?

Square Brackets in MS-SQL Table Designer

In the MS-SQL table designer, you may encounter column names enclosed in square brackets ([]). These brackets serve an important purpose in resolving naming conflicts and ensuring compatibility with other systems.

Delimiter for Reserved Keywords and Special Characters

The primary purpose of square brackets is to delimit identifiers that are either reserved keywords or contain special characters. Reserved keywords are words that have a predefined meaning in the SQL language, such as "TABLE," "WHERE," and "SELECT." Special characters include spaces, hyphens, and symbols.

By enclosing such identifiers in square brackets, you distinguish them from the keywords and prevent any potential conflicts. For instance, the following column name would otherwise be treated as a keyword:

SELECT [SELECT]
FROM TableName

Optional Delimiter for Clarity

Even when an identifier is not a reserved keyword or does not contain special characters, some users prefer to use square brackets for clarity. This practice can help distinguish column names from other elements in the database, such as table names or expressions.

Example from MSDN

According to the Microsoft Developer Network (MSDN), the usage of delimited identifiers is optional for identifiers that adhere to naming conventions, but mandatory for those that do not:

SELECT *
FROM [TableX]         --Delimiter is optional.
WHERE [KeyCol] = 124  --Delimiter is optional.

SELECT *
FROM [My Table]      --Identifier contains a space and uses a reserved keyword.
WHERE [order] = 10   --Identifier is a reserved keyword.

Conclusion

Square brackets in the MS-SQL table designer play a crucial role in handling reserved keywords and special characters in column names. They ensure compatibility with other systems and provide clarity in database design. While their usage is optional for compliant identifiers, it is recommended for clarity and to avoid naming conflicts.

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