About the Firebird 5.0 Language ReferenceData Types and Subtypes

Basic Elements: Statements, Clauses, Keywords

The primary construct in SQL is the statement.A statement defines what the database management system should do with a particular data or metadata object.More complex statements contain simpler constructs — clauses and options.

Clauses

A clause defines a certain type of directive in a statement.For instance, the WHERE clause in a SELECT statement and in other data manipulation statements (e.g. UPDATE, DELETE) specifies criteria for searching one or more tables for the rows that are to be selected, updated or deleted.The ORDER BY clause specifies how the output data — result set — should be sorted.

Options

Options, being the simplest constructs, are specified in association with specific keywords to provide qualification for clause elements.Where alternative options are available, it is usual for one of them to be the default, used if nothing is specified for that option.For instance, the SELECT statement will return all rows that match the search criteria unless the DISTINCT option restricts the output to non-duplicated rows.

Keywords

All words that are included in the SQL lexicon are keywords.Some keywords are reserved, meaning their usage as identifiers for database objects, parameter names or variables is prohibited in some or all contexts.Non-reserved keywords can be used as identifiers, although this is not recommended.From time to time, non-reserved keywords may become reserved, or new (reserved or non-reserved) keywords may be added when new language feature are introduced.Although unlikely, reserved words may also change to non-reserved keywords, or keywords may be removed entirely, for example when parser rules change.

For example, the following statement will be executed without errors because, although ABS is a keyword, it is not a reserved word.

CREATE TABLE T (ABS INT NOT NULL);

On the contrary, the following statement will return an error because ADD is both a keyword and a reserved word.

CREATE TABLE T (ADD INT NOT NULL);

Refer to the list of reserved words and keywords in the chapter Reserved Words and Keywords.

Identifiers

All database objects have names, often called identifiers.The maximum identifier length is 63 characters character set UTF8 (252 bytes).

Note	It is possible to restrict the actual maximum identifier length through configuration.Consult theFirebird 4.0 Release Notesfor details.In this language reference we assume the default configuration of 63 characters (252 bytes).

Two types of names are valid as identifiers: regular identifiers, similar to variable names in regular programming languages, and delimited identifiers that are specific to SQL.To be valid, each type of identifier must conform to a set of rules, as follows:

docnext count = 5

Rules for Regular Identifiers

Length cannot exceed 63 characters
The name must start with an unaccented, 7-bit ASCII alphabetic character.It may be followed by other 7-bit ASCII letters, digits, underscores or dollar signs.No other characters, including spaces, are valid.The name is case-insensitive, meaning it can be declared and used in either upper or lower case.Thus, from the system’s point of view, the following names are the same:
```
fullname
FULLNAME
FuLlNaMe
FullName
```
Regular identifiers are stored in uppercase

Regular name syntax

<name> ::=
  <letter> | <name><letter> | <name><digit> | <name>_ | <name>$

<letter> ::= <upper letter> | <lower letter>

<upper letter> ::= A | B | C | D | E | F | G | H | I | J | K | L | M |
                   N | O | P | Q | R | S | T | U | V | W | X | Y | Z

<lower letter> ::= a | b | c | d | e | f | g | h | i | j | k | l | m |
                   n | o | p | q | r | s | t | u | v | w | x | y | z

<digit> ::= 0 | 1 | 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9

Rules for Delimited Identifiers

Length cannot exceed 63 characters in character set UTF8 (252 bytes).Identifiers are stored in character set UTF8, which means characters outside the ASCII range are stored using 2 to 4 bytes.
The entire string must be enclosed in double-quotes, e.g. "anIdentifier"
A double-quote in an identifier can be escaped by doubling it, e.g. "with""doublequote";we recommend avoiding double-quotes in delimited identifiers.
It may contain any character from the UTF8 character set, including accented characters, spaces and special characters
An identifier can be a reserved word
Delimited identifiers are stored as-is and are case-sensitive in all contexts
Trailing spaces in delimited identifiers are removed, as with any string constant
Delimited identifiers are available in Dialect 3 only.For more details on dialects, see [fblangref50-structure-dialects]

Delimited identifier syntax

<delimited identifier> ::= "<permitted character>[<permitted character> ...]"

Note

A delimited identifier such as "FULLNAME" is the same as the regular identifiers FULLNAME, fullname, FullName, and so on.The reason is that Firebird stores regular identifiers in upper case, regardless of how they were defined or declared.Delimited identifiers are always stored according to the exact case of their definition or declaration.Thus, "FullName" (quoted, or delimited) is different from FullName (unquoted, or regular) which is stored as FULLNAME in the metadata.

Literals

Literals are used to directly represent values in a statement.Examples of standard types of literals are:

integer        - 0, -34, 45, 0X080000000;
fixed-point    - 0.0, -3.14
floating-point - 3.23e-23;
string         - 'text', 'don''t!', Q'{don't!}';
binary string  - x'48656C6C6F20776F726C64'
date           - DATE '2018-01-19';
time           - TIME '15:12:56';
timestamp      - TIMESTAMP '2018-01-19 13:32:02';
boolean        - true, false, unknown
null state     - null

Details about literals for each data type are discussed in section Literals (Constants) of chapter Common Language Elements.

Operators and Special Characters

A set of special characters is reserved for use as operators or separators.

<special char> ::=
  any of <space> or "%&'()*+,-./:;<=>?|^{}

Some of these characters, alone or in combination, may be used as operators (arithmetical, string, logical), as SQL command separators, to quote identifiers, or to mark the limits of string literals or comments.

Operator Syntax

<operator> ::=
    <string concatenation operator>
  | <arithmetic operator>
  | <comparison operator>
  | <logical operator>

<string concatentation operator> ::= '||'

<arithmetic operator> ::= * | / | + | -

<comparison operator> ::=
    =  | <> | != | ~= | ^= | > | < | >= | <=
  | !> | ~> | ^> | !< | ~< | ^<

<logical operator> ::= NOT | AND | OR

For more details on operators, see Expressions.

Comments

Comments may be present in SQL scripts, SQL statements and PSQL modules.A comment can be any text, usually used to document how particular parts of the code work.The parser ignores the text of comments.

Firebird supports two types of comments: block (or bracketed) and in-line (or simple).

Syntax

<comment> ::= <block comment> | <single-line comment>

<block comment> ::=
  /* <character>[<character> ...] */

<single-line comment> ::=
  -- <character>[<character> ...]<end line>

Block comments start with the /* character pair and end with the */ character pair.Text in block comments may be of any length and can occupy multiple lines.

In-line comments start with a pair of hyphen characters, -- and continue until the first linebreak (end of line).

Example

CREATE PROCEDURE P(APARAM INT)
  RETURNS (B INT)
AS
BEGIN
  /* This text will be ignored during the execution of the statement
     since it is a comment
  */
  B = A + 1; -- In-line comment
  SUSPEND;
END