Know Difference between Oracle Reserved Words and Keywords

与C和JAVA体系类似,Oracle中存在一些保留词(Reserved Words)或关键词(Keywords)以及少量的命名空间(Namespace)。

保留词(Reserved Words)是优先级最高的词汇，在Oracle中这些词都有着特殊的意义。所以这些词不允许被重定义 (redefine),换而言之就不是不允许用作对象的名字。以下为Oracle 10g中保留词的列表:

Oracle Reserved Words
ACCESS	ELSE	MODIFY	START
ADD	EXCLUSIVE	NOAUDIT	SELECT
ALL	EXISTS	NOCOMPRESS	SESSION
ALTER	FILE	NOT	SET
AND	FLOAT	NOTFOUND	SHARE
ANY	FOR	NOWAIT	SIZE
ARRAYLEN	FROM	NULL	SMALLINT
AS	GRANT	NUMBER	SQLBUF
ASC	GROUP	OF	SUCCESSFUL
AUDIT	HAVING	OFFLINE	SYNONYM
BETWEEN	IDENTIFIED	ON	SYSDATE
BY	IMMEDIATE	ONLINE	TABLE
CHAR	IN	OPTION	THEN
CHECK	INCREMENT	OR	TO
CLUSTER	INDEX	ORDER	TRIGGER
COLUMN	INITIAL	PCTFREE	UID
COMMENT	INSERT	PRIOR	UNION
COMPRESS	INTEGER	PRIVILEGES	UNIQUE
CONNECT	INTERSECT	PUBLIC	UPDATE
CREATE	INTO	RAW	USER
CURRENT	IS	RENAME	VALIDATE
DATE	LEVEL	RESOURCE	VALUES
DECIMAL	LIKE	REVOKE	VARCHAR
DEFAULT	LOCK	ROW	VARCHAR2
DELETE	LONG	ROWID	VIEW
DESC	MAXEXTENTS	ROWLABEL	WHENEVER
DISTINCT	MINUS	ROWNUM	WHERE
DROP	MODE	ROWS	WITH

注意虽然我们不能直接将保留词用于对象名，但还是可以通过特殊手段来完成这种不推荐的定义目的，如:

如上表所列START为一个保留词
SQL> CREATE TABLE START (T1 INT);

CREATE TABLE START (T1 INT)

ORA-00903: invalid table name

利用双引号可以成功将保留词用作对象名,但是在管理时会很麻烦,极力不推荐!

SQL> CREATE TABLE "START" (T1 INT);

Table created

SQL> SELECT * FROM START;

SELECT * FROM START

ORA-00903: invalid table name

SQL> SELECT * FROM "START";

T1
---------------------------------------

SQL> SELECT * FROM "start";

SELECT * FROM "start"

ORA-00942: table or view does not exist

SQL> select object_name from dba_objects where object_name='START';

OBJECT_NAME
--------------------------------------------------------------------------------
START

SQL> DROP TABLE "start";

DROP TABLE "start"

ORA-00942: table or view does not exist

SQL> DROP TABLE "START";

Table dropped

关键词同样是在Oracle中具有特殊意义的词汇，但是其可以用作重定义(redefine)。Oracle文档介绍这些关键词可能在今后的版本中变成保留词。以下为Oracle 10g中关键词的列表:

Oracle Keywords
ADMIN	CURSOR	FOUND	MOUNT
AFTER	CYCLE	FUNCTION	NEXT
ALLOCATE	DATABASE	GO	NEW
ANALYZE	DATAFILE	GOTO	NOARCHIVELOG
ARCHIVE	DBA	GROUPS	NOCACHE
ARCHIVELOG	DEC	INCLUDING	NOCYCLE
AUTHORIZATION	DECLARE	INDICATOR	NOMAXVALUE
AVG	DISABLE	INITRANS	NOMINVALUE
BACKUP	DISMOUNT	INSTANCE	NONE
BEGIN	DOUBLE	INT	NOORDER
BECOME	DUMP	KEY	NORESETLOGS
BEFORE	EACH	LANGUAGE	NORMAL
BLOCK	ENABLE	LAYER	NOSORT
BODY	END	LINK	NUMERIC
CACHE	ESCAPE	LISTS	OFF
CANCEL	EVENTS	LOGFILE	OLD
CASCADE	EXCEPT	MANAGE	ONLY
CHANGE	EXCEPTIONS	MANUAL	OPEN
CHARACTER	EXEC	MAX	OPTIMAL
CHECKPOINT	EXPLAIN	MAXDATAFILES	OWN
CLOSE	EXECUTE	MAXINSTANCES	PACKAGE
COBOL	EXTENT	MAXLOGFILES	PARALLEL
COMMIT	EXTERNALLY	MAXLOGHISTORY	PCTINCREASE
COMPILE	FETCH	MAXLOGMEMBERS	PCTUSED
CONSTRAINT	FLUSH	MAXTRANS	PLAN
CONSTRAINTS	FREELIST	MAXVALUE	PLI
CONTENTS	FREELISTS	MIN	PRECISION
CONTINUE	FORCE	MINEXTENTS	PRIMARY
CONTROLFILE	FOREIGN	MINVALUE	PRIVATE
COUNT	FORTRAN	MODULE	PROCEDURE
PROFILE	SAVEPOINT	SQLSTATE	TRACING
QUOTA	SCHEMA	STATEMENT_ID	TRANSACTION
READ	SCN	STATISTICS	TRIGGERS
REAL	SECTION	STOP	TRUNCATE
RECOVER	SEGMENT	STORAGE	UNDER
REFERENCES	SEQUENCE	SUM	UNLIMITED
REFERENCING	SHARED	SWITCH	UNTIL
RESETLOGS	SNAPSHOT	SYSTEM	USE
RESTRICTED	SOME	TABLES	USING
REUSE	SORT	TABLESPACE	WHEN
ROLE	SQL	TEMPORARY	WRITE
ROLES	SQLCODE	THREAD	WORK
ROLLBACK	SQLERROR	TIME

Pl/SQL中还有部分的保留词(PL/SQL Reserved Words),在嵌入SQL语句需要对这些词汇特殊处理。

PL/SQL Reserved Words
ABORT	BETWEEN	CRASH	DIGITS
ACCEPT	BINARY_INTEGER	CREATE	DISPOSE
ACCESS	BODY	CURRENT	DISTINCT
ADD	BOOLEAN	CURRVAL	DO
ALL	BY	CURSOR	DROP
ALTER	CASE	DATABASE	ELSE
AND	CHAR	DATA_BASE	ELSIF
ANY	CHAR_BASE	DATE	END
ARRAY	CHECK	DBA	ENTRY
ARRAYLEN	CLOSE	DEBUGOFF	EXCEPTION
AS	CLUSTER	DEBUGON	EXCEPTION_INIT
ASC	CLUSTERS	DECLARE	EXISTS
ASSERT	COLAUTH	DECIMAL	EXIT
ASSIGN	COLUMNS	DEFAULT	FALSE
AT	COMMIT	DEFINITION	FETCH
AUTHORIZATION	COMPRESS	DELAY	FLOAT
AVG	CONNECT	DELETE	FOR
BASE_TABLE	CONSTANT	DELTA	FORM
BEGIN	COUNT	DESC	FROM
FUNCTION	NEW	RELEASE	SUM
GENERIC	NEXTVAL	REMR	TABAUTH
GOTO	NOCOMPRESS	RENAME	TABLE
GRANT	NOT	RESOURCE	TABLES
GROUP	NULL	RETURN	TASK
HAVING	NUMBER	REVERSE	TERMINATE
IDENTIFIED	NUMBER_BASE	REVOKE	THEN
IF	OF	ROLLBACK	TO
IN	ON	ROWID	TRUE
INDEX	OPEN	ROWLABEL	TYPE
INDEXES	OPTION	ROWNUM	UNION
INDICATOR	OR	ROWTYPE	UNIQUE
INSERT	ORDER	RUN	UPDATE
INTEGER	OTHERS	SAVEPOINT	USE
INTERSECT	OUT	SCHEMA	VALUES
INTO	PACKAGE	SELECT	VARCHAR
IS	PARTITION	SEPARATE	VARCHAR2
LEVEL	PCTFREE	SET	VARIANCE
LIKE	POSITIVE	SIZE	VIEW
LIMITED	PRAGMA	SMALLINT	VIEWS
LOOP	PRIOR	SPACE	WHEN
MAX	PRIVATE	SQL	WHERE
MIN	PROCEDURE	SQLCODE	WHILE
MINUS	PUBLIC	SQLERRM	WITH
MLSLABEL	RAISE	START	WORK
MOD	RANGE	STATEMENT	XOR
MODE	REAL	STDDEV
NATURAL	RECORD	SUBTYPE

除去保留词和关键词外,Oracle内部还存在一张命名空间(namespace)的列表，这些命名空间或为OCI函数或为Oracle内部函数作为函数的起始字符，如SQL*NET透明网络服务相关函数都以"NS"为函数名的开头，Oracle不推荐使用用户函数使用这些保留的命名空间为开头，以避免潜在的冲突可能。

Oracle Reserved Namespaces

Namespace	Library
O	OCI functions
S	function names from SQLLIB and system-dependent libraries
XA	external functions for XA applications only
GEN KP L NA NC ND NL NM NR NS NT NZ TTC UPI	Internal functions