Identifiers are the names of databases, tables, or columns that you specify in a SQL statement. The rules for identifiers govern what names you can give to things you create, the notation for referring to names containing unusual characters, and other aspects such as case sensitivity.

• The minimum length of an identifier is 1 character.
• The maximum length of an identifier is currently 128 characters, enforced by the metastore database.
• An identifier must start with an alphabetic character. The remainder can contain any combination of alphanumeric characters and underscores. Quoting the identifier with backticks has no effect on the allowed characters in the name.
• An identifier can contain only ASCII characters.
• To use an identifier name that matches one of the Impala reserved keywords (listed in Appendix C - Impala Reserved Words), surround the identifier with `` characters (backticks).
• Impala identifiers are always case-insensitive. That is, tables named t1 and T1 always refer to the same table, regardless of quote characters. Internally, Impala always folds all specified table and column names to lowercase. This is why the column headers in query output are always displayed in lowercase.

See Aliases for how to define shorter or easier-to-remember aliases if the original names are long or cryptic identifiers. Aliases follow the same rules as identifiers when it comes to case insensitivity. Aliases can be longer than identifiers (up to the maximum length of a Java string) and can include additional characters such as spaces and dashes when they are quoted using backtick characters.

Another way to define different names for the same tables or columns is to create views. See Views for details.