Significance of Square Brackets [] in T-SQL Code

After one of my T-SQL presentations, I was asked about the significance of square brackets around objects in T-SQL. I had an idea of their purpose but to confirm I asked T-SQL guru, Itzik Ben-Gan.

Basically he highlighted the fact that a database object name is known as its identifier (e.g., a name of a column, table, etc.) and it can be either regular or irregular.

When the identifier is regular, delimiting it is optional but when the identifier is irregular (e.g., starts with a digit, has a space within it, is a reserved keyword, etc.), it has to be delimited.

T-SQL supports two kinds of delimiters:

1. Square brackets, e.g., [Order Details], which is proprietary.
2. Double quotes, e.g., "Order Details", which is standard.

Both delimiters for irregular identifiers results in no errors

No delimiters for irregular identifiers results in errors

If you want to know what makes an identifier regular then check here under “Rules for Regular Identifiers”.