SQL manipulates sets of data. The language is composed of various key words. 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.
SQL92 defines key words for the language which have specific meaning. Some key words are reserved, which indicates that they are restricted to appear in only certain contexts. Other key words are not restricted, which indicates that in certain contexts they have a specific meaning but are not otherwise constrained.
Postgres implements an extended subset of the SQL92 and SQL3 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 Postgres.
Information on SQL92 and SQL3 key words is derived from Date and Darwen, 1997.
SQL92 and SQL3 have reserved key words which are not allowed as identifiers and not allowed in any usage other than as fundamental tokens in SQL statements. Postgres 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: Any string can be specified as an identifier if surrounded by double quotes (“like this!”). Some care is required since such an identifier will be case sensitive and will retain embedded whitespace other special characters.
The following are Postgres reserved words which are neither SQL92 nor SQL3 reserved words. These are allowed to be present as column labels, but not as identifiers:
ABORT ANALYZE
BINARY
CLUSTER CONSTRAINT COPY
DO
EXPLAIN EXTEND
LISTEN LOAD LOCK
MOVE
NEW NONE NOTIFY
RESET
SETOF SHOW
UNLISTEN UNTIL
VACUUM VERBOSE
The following are Postgres reserved words which are also SQL92 or SQL3 reserved words, and which are allowed to be present as column labels, but not as identifiers:
CASE COALESCE CROSS CURRENT
ELSE END
FALSE FOREIGN
GLOBAL GROUP
LOCAL
NULLIF
ORDER
POSITION PRECISION
TABLE THEN TRANSACTION TRUE
WHEN
The following are Postgres reserved words which are also SQL92 or SQL3 reserved words: 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
The following are SQL92 reserved key words which are not Postgres reserved key words, but which if used as function names are always translated into the function length:
CHAR_LENGTH CHARACTER_LENGTH
The following are SQL92 or SQL3 reserved key words which are not Postgres reserved key words, but if used as type names are always translated into an alternate, native type:
BOOLEAN DOUBLE FLOAT INT INTEGER INTERVAL REAL SMALLINT
The following are either SQL92 or SQL3 reserved key words which are not key words in Postgres. These have no proscribed usage in Postgres at the time of writing (v6.5) but may become reserved key words in the future:
Note: Some of these key words represent functions in SQL92. These functions are defined in Postgres, but the parser does not consider the names to be key words and they are allowed in other contexts.
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
SQL92 and SQL3 have non-reserved keywords which have a proscribed meaning in the language but which are also allowed as identifiers. Postgres has additional keywords which allow similar unrestricted usage. In particular, these keywords are allowed as column or table names.
The following are Postgres non-reserved key words which are neither SQL92 nor SQL3 non-reserved key words:
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
The following are Postgres non-reserved key words which are SQL92 or SQL3 reserved key words:
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
The following are Postgres non-reserved key words which are also either SQL92 or SQL3 non-reserved key words:
COMMITTED SERIALIZABLE TYPE
The following are either SQL92 or SQL3 non-reserved key words which are not key words of any kind in Postgres:
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