What is the difference between square brackets and single quotes for aliasing in SQL Server?

Question

I have seen some people alias column names using single quotes eg:

select orderID \'Order No\' from orders

and others use square brackets e

Answer 1

It depends on what settings you have in force whether 's are valid or not. And you missed out ". See Delimited Identifiers:

When QUOTED_IDENTIFIER is set to ON, SQL Server follows the ISO rules for the use of double quotation marks (")and the single quotation mark (') in SQL statements. For example:

• Double quotation marks can be used only to delimit identifiers. They cannot be used to delimit character strings.

• Single quotation marks must be used to enclose character strings. They cannot be used to delimit identifiers.

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When QUOTED_IDENTIFIER is set to OFF, SQL Server uses the following rules for single and double quotation marks:

• Quotation marks cannot be used to delimit identifiers. Instead, brackets have to be used as delimiters.

• Single or double quotation marks can be used to enclose character strings.

And finally:

Delimiters in brackets can always be used, regardless of the setting of QUOTED_IDENTIFIER

Where, in all of the above quotes, when they refer to brackets they're talking about [] brackets.