Identifiers

IDENTIFIERS:

It must consist of a combination of 1 through 128 letters, digits or the symbols
#, $ @ or _.

If we set QUOTED IDENTIFIER ON, we can use keywords as objects names (ex: columns
names).

A column of type rowversion holds an internal sequence number that SQL Server automatically
updates every time the row is modified.

Identifiers(Topic Covered from MSDN): The database object name
is referred to as its identifier.

Everything in Microsoft SQL Server can have an identifier. Servers, databases, and
database objects, such as tables, views, columns, indexes, triggers, procedures,
constraints, and rules, can have identifiers. Identifiers are required for most
objects, but are optional for some objects such as constraints. An object identifier
is created when the object is defined. The identifier is then used to reference
the object.

For example, the following statement creates a table with the identifier TableX,
and two columns with the identifiers KeyCol and Description:

CREATE TABLE TableX (KeyCol INT PRIMARY KEY, Description nvarchar(80))

This table also has an unnamed constraint. The PRIMARY KEY constraint has no identifier.
The collation of an identifier depends on the level at which it is defined. Identifiers
of instance-level objects, such as logins and database names, are assigned the default
collation of the instance. Identifiers of objects in a database, such as tables,
views, and column names, are assigned the default collation of the database.

For example, two tables with names that differ only in case can be created in a
database that has case-sensitive collation, but cannot be created in a database
that has case-insensitive collation.

Classes of Identifiers

There are two classes of identifiers:

Regular identifiers

Comply with the rules for the format of identifiers. Regular identifiers are not
delimited when they are used in Transact-SQL statements.

SELECT * FROM TableX WHERE KeyCol = 124

Delimited identifiers

Are enclosed in double quotation marks (") or brackets ([ ]). Identifiers that comply
with the rules for the format of identifiers might not be delimited. For example:

SELECT * FROM [TableX] --Delimiter is optional.

WHERE [KeyCol] = 124 --Delimiter is optional.

Identifiers that do not comply with all the rules for identifiers must be delimited
in a Transact-SQL statement.

For example:

SELECT * FROM [My Table] --Identifier contains a space and uses a reserved keyword.

WHERE [order] = 10 --Identifier is a reserved keyword.

Both regular and delimited identifiers must contain from 1 through 128 characters.
For local temporary tables, the identifier can have a maximum of 116 characters.