Tokens such as SELECT
, or VALUES
in the example above are examples of key words
, that is, words that have a fixed meaning in the SQL
language. The tokens MY_TABLE
are examples of identifiers
. They identify names of tables, columns, or other database objects, depending on the command they are used in. Therefore they are sometimes simply called, “names
”. Key words and identifiers have the same lexical structure
, meaning that one cannot know whether a token is an identifier or a key word without knowing the language.
identifiers and key words must begin with a letter (a-z
). Subsequent characters in an identifier or key word can be letters, underscores, digits (0-9
), dollar signs ($
), or number signs (#
There is a second kind of identifier: the delimited identifier
or quoted identifier
. It is formed by enclosing an arbitrary sequence of characters in double-quotes ("
). A delimited identifier is always an identifier, never a key word. So "select"
could be used to refer to a column or table named "select"
, whereas an unquoted select would be taken as a key word and would therefore provoke a parse error when used where a table or column name is expected. The example can be written with quoted identifiers like this: