Why Are Square Brackets Used in MS-SQL Table Column Names?

Square Brackets in MS-SQL Table Designer: Understanding Their Significance

In the context of MS-SQL table design, square brackets [] play a crucial role in identifying columns. While exploring a copy of an existing database, you may encounter column names enclosed in square brackets. This has prompted the question about the purpose and implications of such notation.

Purpose of Square Brackets in MS-SQL

Square brackets serve the following purposes in MS-SQL:

1. Delimiting Identifiers:
   They are used to enclose column names that contain special characters or are reserved keywords. This ensures that these names are interpreted as valid identifiers by the database engine.
2. Optional Use:
   While delimiting identifiers with square brackets is not always necessary, some users prefer to use it even for compliant identifiers. This provides consistency and ensures unambiguous identification.

Example:

As per the Microsoft Developer Network (MSDN), delimited identifiers are enclosed in double quotation marks (") or square brackets ([]).

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

Identifiers containing special characters or reserved keywords must be delimited in Transact-SQL statements.

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

Additional Information:

• The use of square brackets for delimiting identifiers aligns with the Transact-SQL rules for identifier formatting.
• Delimitation ensures clarity and avoids potential conflicts when working with tables that contain columns with unconventional names.
• It's important to note that square brackets do not indicate any special data type or column property in MS-SQL.

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