SQLServer Identifier
Unquoted identifiers
Unquoted identifiers can use letters (a-z), digits (0-9), and underscore (_), and must start with a letter.
Depending on SQL implementation, and/or database settings, other characters may be allowed, some even as the first character, e.g.
.MS SQL: @, $, #, and other Unicode letters
.MySQL: $
.Oracle: $, #, and other letters from database character set
.PostgreSQL: $, and other Unicode letters
Unquoted identifiers are case-insensitive. How this is handled depends greatly on SQL implementation:
.MS SQL: Case-preserving, sensitivity defined by database character set, so can be case-sensitive.
.MySQL: Case-preserving, sensitivity depends on database setting and underlying file system.
.Oracle: Converted to uppercase, then handled like quoted identifier.
.PostgreSQL: Converted to lowercase, then handled like quoted identifier.
.SQLite: Case-preserving; case insensitivity only for ASCII characters.