Identifiers

Identifiers are the names of tables, columns and other metadata elements used in a SQL query.

Unquoted identifiers, such as emp, must start with a letter and can only contain letters, digits, and underscores. They are implicitly converted to upper case.

Quoted identifiers, such as "Employee Name", start and end with double quotes. They may contain virtually any character, including spaces and other punctuation. If you wish to include a double quote in an identifier, use another double quote to escape it, like this: "An employee called ""Fred"".".

Quoting an identifier also makes it case-sensitive, whereas unquoted names are always folded to upper case.

A variant of quoted identifiers allows including escaped Unicode characters identified by their code points. This variant starts with U& (upper or lower case U followed by ampersand) immediately before the opening double quote, without any spaces in between, for example U&"foo". Inside the quotes, Unicode characters can be specified in escaped form by writing a backslash followed by the four-digit hexadecimal code point number. For example, the identifier "data" could be written as

U&"d\0061t\0061"

If a different escape character than backslash is desired, it can be specified using the UESCAPE clause after the string, for example using ! as the escape character:

U&"d!0061t!0061" UESCAPE '!'

The escape character can be any single character other than a hexadecimal digit, the plus sign, a single quote, a double quote, or a whitespace character. Note that the escape character is written in single quotes, not double quotes, after UESCAPE.

To include the escape character in the identifier literally, write it twice.

Comments

A comment is a sequence of characters beginning with double dashes and extending to the end of the line, e.g.:

-- This is a standard SQL comment

Alternatively, C-style block comments can be used:

/* multiline comment
 * with nesting: /* nested block comment */
 */

where the comment begins with /* and extends to the matching occurrence of */. Note that block comments cannot be nested unlike the requirements of the SQL standard.