What is the use of the square brackets [] in sql s

问题:

I've noticed that Visual Studio 2008 is placing square brackets around column names in sql. Do the brackets offer any advantage? When I hand code T-SQL I've never bothered with them.

Example: Visual Studio: SELECT [column1], [column2] etc...

My own way: SELECT column1, column2 etc...

回答1:

The brackets are required if you use keywords or special chars in the column names or identifiers. You could name a column [First Name] (with a space)--but then you'd need to use brackets every time you referred to that column.

The newer tools add them everywhere just in case or for consistency.

回答2:

They're handy if your columns have the same names as SQL keywords, or have spaces in them.

Example:

create table test ( id int, user varchar(20) )

Oh no! Incorrect syntax near the keyword 'user'. But this:

create table test ( id int, [user] varchar(20) )

Works fine.

回答3:

They are useful if you are (for some reason) using column names with certain characters for example.

Select First Name From People

would not work, but putting square brackets around the column name would work

Select [First Name] From People

In short, it's a way of explicitly declaring a object name; column, table, database, user or server.

回答4:

Column names can contain characters and reserved words that will confuse the query execution engine, so placing brackets around them at all times prevents this from happening. Easier than checking for an issue and then dealing with it, I guess.

回答5:

The brackets can be used when column names are reserved words.

If you are programatically generating the SQL statement from a collection of column names you don't control, then you can avoid problems by always using the brackets.

回答6:

In addition Some Sharepoint databases contain hyphens in their names. Using square brackets in SQL Statements allow the names to be parsed correctly.

回答7:

I believe it adds them there for consistency... they're only required when you have a space or special character in the column name, but it's cleaner to just include them all the time when the IDE generates SQL.

回答8:

Regardless of following a naming convention that avoids using reserved words, Microsoft does add new reserved words. Using brackets allows your code to be upgraded to a new SQL Server version, without first needing to edit Microsoft's newly reserved words out of your client code. That editing can be a significant concern. It may cause your project to be prematurely retired....

Brackets can also be useful when you want to Replace All in a script. If your batch contains a variable named @String and a column named [String], you can rename the column to [NewString], without renaming @String to @NewString.

回答9:

During the dark ages of SQL in the 1990ths it was a good practice as the SQL designers were trying to add each word in the dictionary as keyword for endless avalanche of new features and they called it the SQL3 draft.

So it keeps forward compatibility.

And i found that it has another nice side effect, it helps a lot when you use grep in code reviews and refactoring.