<chapter id="syntax">
<title>SQL Syntax</title>

<sect1>
<title>Key Words</title>

<para>
<acronym>SQL92</acronym> defines <firstterm>key words</firstterm> 
for the language
which have specific meaning. Some key words are
<firstterm>reserved</firstterm>, which indicates that they are
restricted to appear in only certain contexts. Other key words are
<firstterm>not restricted</firstterm>, which indicates that in certain 
contexts they
have a specific meaning but are not otherwise constrained.

<para>
<productname>Postgres</productname> implements an extended subset of the
<acronym>SQL92</acronym> and <acronym>SQL3</acronym> languages. Some language
elements are not as restricted in this implementation as is
called for in the language standards, in part due
to the extensibility features of <productname>Postgres</productname>. 

<para>
Information on <acronym>SQL92</acronym> and <acronym>SQL3</acronym> key words
is derived from <xref linkend="DATE97" endterm="DATE97-full">.

<Sect2>
<Title>Reserved Key Words</Title>

<Para>
<acronym>SQL92</acronym> and <acronym>SQL3</acronym> have 
<firstterm>reserved key words</firstterm> which are not allowed 
as identifiers and not allowed in any usage other than as fundamental
tokens in <acronym>SQL</acronym> statements.
<productname>Postgres</productname> has additional key words
which have similar restrictions. In particular, these key words
are not allowed as column or table names, though in some cases
they are allowed to be column labels (i.e. in AS clauses).

<tip>
<para>
Any string can be specified as an identifier if surrounded by
double quotes (<quote>like this!</quote>). Some care is required since
such an identifier will be case sensitive
and will retain embedded whitespace other special characters.
</tip>

<para>
The following are <productname>Postgres</productname>
reserved words which are neither <acronym>SQL92</acronym>
nor <acronym>SQL3</acronym> reserved words. These are allowed
to be present as column labels, but not as identifiers:

<programlisting>
ABORT ANALYZE 
BINARY 
CLUSTER CONSTRAINT COPY
DO 
EXPLAIN EXTEND
LISTEN LOAD LOCK 
MOVE 
NEW NONE NOTIFY 
RESET 
SETOF SHOW
UNLISTEN UNTIL 
VACUUM VERBOSE
</programlisting>

The following are <productname>Postgres</productname>
reserved words which are also <acronym>SQL92</acronym> 
or <acronym>SQL3</acronym> reserved words, and which
are allowed to be present as column labels, but not as identifiers:

<programlisting>
CROSS CURRENT 
FALSE FOREIGN 
GROUP 
ORDER 
POSITION PRECISION 
TABLE TRANSACTION TRUE
</programlisting>

The following are <productname>Postgres</productname>
reserved words which are also <acronym>SQL92</acronym> 
or <acronym>SQL3</acronym> reserved words:

<programlisting>
ADD ALL ALTER AND ANY AS ASC
BEGIN BETWEEN BOTH BY
CASCADE CAST CHAR CHARACTER CHECK CLOSE COLLATE COLUMN COMMIT 
CONSTRAINT CREATE CURRENT_DATE CURRENT_TIME 
CURRENT_TIMESTAMP CURRENT_USER CURSOR
DECIMAL DECLARE DEFAULT DELETE DESC DISTINCT DROP
END EXECUTE EXISTS EXTRACT
FETCH FLOAT FOR FROM FULL
GRANT 
HAVING
IN INNER INSERT INTERVAL INTO IS
JOIN 
LEADING LEFT LIKE LOCAL
NAMES NATIONAL NATURAL NCHAR NO NOT NULL NUMERIC
ON OR OUTER
PARTIAL PRIMARY PRIVILEGES PROCEDURE PUBLIC
REFERENCES REVOKE RIGHT ROLLBACK
SELECT SET SUBSTRING
TO TRAILING TRIM 
UNION UNIQUE UPDATE USER USING
VALUES VARCHAR VARYING VIEW
WHERE WITH WORK 
</programlisting>

The following are <acronym>SQL92</acronym> reserved key words which
are not <productname>Postgres</productname> reserved key words, but which
if used as function names are always translated into the function
<function>length</function>:

<programlisting>
CHAR_LENGTH CHARACTER_LENGTH
</programlisting>

The following are <acronym>SQL92</acronym> or <acronym>SQL3</acronym> 
reserved key words which
are not <productname>Postgres</productname> reserved key words, but
if used as type names which are always translated into an alternate, native type:

<programlisting>
BOOLEAN DOUBLE FLOAT INT INTEGER INTERVAL REAL SMALLINT
</programlisting>

<para>
The following are either <acronym>SQL92</acronym>
or <acronym>SQL3</acronym> reserved key words
which are not key words in <productname>Postgres</productname>.
These have no proscribed usage in <productname>Postgres</productname>
at the time of writing (v6.4) but may become reserved key words in the
future:

<note>
<para>
Some of these key words represent functions in <acronym>SQL92</acronym>.
These functions are defined in <productname>Postgres</productname>,
but the parser does not consider the names to be key words and they are allowed
in other contexts.
</note>

<programlisting>
ALLOCATE ARE ASSERTION AT AUTHORIZATION AVG 
BIT BIT_LENGTH
CASCADED CASE CATALOG COALESCE COLLATION
CONNECT CONNECTION CONSTRAINTS CONTINUE CONVERT CORRESPONDING COUNT
DATE DEALLOCATE DEC DESCRIBE DESCRIPTOR DIAGNOSTICS DISCONNECT DOMAIN 
ELSE END-EXEC ESCAPE EXCEPT EXCEPTION EXEC EXTERNAL 
FIRST FOUND
GET GLOBAL GO GOTO 
IDENTITY IMMEDIATE INDICATOR INITIALLY INPUT INTERSECT ISOLATION 
LAST LEVEL LOWER 
MAX MIN MODULE 
NULLIF
OCTET_LENGTH OPEN OUTPUT OVERLAPS 
PREPARE PRESERVE 
RESTRICT ROWS
SCHEMA SECTION SESSION SESSION_USER SIZE SOME 
SQL SQLCODE SQLERROR SQLSTATE SUM SYSTEM_USER
TEMPORARY THEN TRANSLATE TRANSLATION 
UNKNOWN UPPER USAGE
VALUE 
WHEN WHENEVER WRITE
</programlisting>

<Sect2>
<Title>Non-reserved Keywords</Title>

<Para>
<acronym>SQL92</acronym> and <acronym>SQL3</acronym> have 
<firstterm>non-reserved keywords</firstterm> which have
a proscribed meaning in the language but which are also allowed
as identifiers.
<productname>Postgres</productname> has additional keywords
which allow similar unrestricted usage.
In particular, these keywords
are allowed as column or table names.

<para>
The following are <productname>Postgres</productname>
non-reserved key words which are neither <acronym>SQL92</acronym>
nor <acronym>SQL3</acronym> non-reserved key words:

<programlisting>
AFTER AGGREGATE 
BACKWARD BEFORE 
CACHE CREATEDB CREATEUSER CYCLE
DATABASE DELIMITERS 
EACH ENCODING 
FORWARD FUNCTION 
HANDLER
INCREMENT INDEX INHERITS INSENSITIVE INSTEAD ISNULL
LANCOMPILER LOCATION 
MAXVALUE MINVALUE
NOCREATEDB NOCREATEUSER NOTHING NOTNULL 
OIDS OPERATOR 
PASSWORD PROCEDURAL
RECIPE RENAME  RETURNS ROW RULE
SEQUENCE SERIAL START STATEMENT STDIN STDOUT 
TRUSTED 
VALID VERSION
</programlisting>

<para>
The following are <productname>Postgres</productname>
non-reserved key words which are <acronym>SQL92</acronym>
or <acronym>SQL3</acronym> reserved key words:

<programlisting>
ABSOLUTE ACTION
DAY
HOUR
INSENSITIVE 
KEY 
LANGUAGE 
MATCH MINUTE MONTH
NEXT 
OF ONLY OPTION 
PRIOR PRIVILEGES 
READ RELATIVE 
SCROLL SECOND
TIME TIMESTAMP TIMEZONE_HOUR TIMEZONE_MINUTE TRIGGER 
YEAR
ZONE
</programlisting>

<para>
The following are <productname>Postgres</productname>
non-reserved key words which are also either <acronym>SQL92</acronym>
or <acronym>SQL3</acronym> non-reserved key words:

<programlisting>
TYPE
</programlisting>

<para>
The following are either <acronym>SQL92</acronym>
or <acronym>SQL3</acronym> non-reserved key words which are not
key words of any kind in <productname>Postgres</productname>:

<programlisting>
ADA
C CATALOG_NAME CHARACTER_SET_CATALOG CHARACTER_SET_NAME 
CHARACTER_SET_SCHEMA CLASS_ORIGIN COBOL COLLATION_CATALOG
COLLATION_NAME COLLATION_SCHEMA COLUMN_NAME
COMMAND_FUNCTION COMMITTED CONDITION_NUMBER
CONNECTION_NAME CONSTRAINT_CATALOG CONSTRAINT_NAME
CONSTRAINT_SCHEMA CURSOR_NAME
DATA DATE_TIME_INTERVAL_CODE DATE_TIME_INTERVAL_PRECISION
DYNAMIC_FUNCTION
FORTRAN
LENGTH
MESSAGE_LENGTH MESSAGE_OCTET_LENGTH MORE MUMPS
NAME NULLABLE NUMBER
PAD PASCAL PLI
REPEATABLE RETURNED_LENGTH RETURNED_OCTET_LENGTH
RETURNED_SQLSTATE ROW_COUNT
SCALE SCHEMA_NAME SERIALIZABLE SERVER_NAME SPACE
SUBCLASS_ORIGIN
TABLE_NAME
UNCOMMITTED UNNAMED
</programlisting>
