 <chapter>
  <title>SQL Syntax</title>

  <abstract>
   <para>
    <acronym>SQL</acronym> manipulates sets of data. The language is
    composed of various <firstterm>key words</firstterm>. Arithmetic
    and procedural expressions are allowed. We will cover these topics
    in this chapter; subsequent chapters will include details on data
    types, functions, and operators.
   </para>
  </abstract>

  <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>

   <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>

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

   <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).
    </para>

    <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.
     </para>
    </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>
    </para>

    <para>
     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>
CASE COALESCE CROSS CURRENT 
ELSE END
FALSE FOREIGN 
GLOBAL GROUP 
LOCAL
NULLIF
ORDER 
POSITION PRECISION 
TABLE THEN TRANSACTION TRUE
WHEN
     </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
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>
    </para>

    <para>
     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>
    </para>

    <para>
     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 are always translated into an alternate, native type:

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

    <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 (v6.5) 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.
      </para>
     </note>

     <programlisting>
ALLOCATE ARE ASSERTION AT AUTHORIZATION AVG 
BIT BIT_LENGTH
CASCADED CATALOG COLLATION CONNECT CONNECTION
 CONSTRAINTS CONTINUE CONVERT CORRESPONDING COUNT
DATE DEALLOCATE DEC DESCRIBE DESCRIPTOR DIAGNOSTICS DISCONNECT DOMAIN 
END-EXEC ESCAPE EXCEPT EXCEPTION EXEC EXTERNAL 
FIRST FOUND
GET GO GOTO 
IDENTITY IMMEDIATE INDICATOR INITIALLY INPUT INTERSECT ISOLATION 
LAST LEVEL LOWER 
MAX MIN MODULE 
OCTET_LENGTH OPEN OUTPUT OVERLAPS 
PREPARE PRESERVE 
RESTRICT ROWS
SCHEMA SECTION SESSION SESSION_USER SIZE SOME 
 SQL SQLCODE SQLERROR SQLSTATE SUM SYSTEM_USER
TEMPORARY TRANSLATE TRANSLATION 
UNKNOWN UPPER USAGE
VALUE 
WHENEVER WRITE
     </programlisting>
    </para>
   </sect2>

   <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>

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

    <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>

    <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>
COMMITTED SERIALIZABLE TYPE
     </programlisting>
    </para>

    <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 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 SERVER_NAME SPACE
SUBCLASS_ORIGIN
TABLE_NAME
UNCOMMITTED UNNAMED
     </programlisting>
    </para>
   </sect2>
  </sect1>

  <sect1>
   <title>Expressions</title>

   <para>
    <acronym>SQL92</acronym> allows <firstterm>expressions</firstterm>
    to transform data in expressions. Expressions may contain operators
    (see <xref linkend="operators-title" endterm="operators-title">
    for more details) and functions
    (<xref linkend="functions-title" endterm="functions-title"> has
    more information).

   </para>
  </sect1>
 </chapter>

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