C. SQL 關鍵字

Table C.1 lists all tokens that are key words in the SQL standard and in PostgreSQL 11devel. Background information can be found in Section 4.1.1. (For space reasons, only the latest two versions of the SQL standard, and SQL-92 for historical comparison, are included. The differences between those and the other intermediate standard versions are small.)

SQL distinguishes between reserved and non-reserved key words. According to the standard, reserved key words are the only real key words; they are never allowed as identifiers. Non-reserved key words only have a special meaning in particular contexts and can be used as identifiers in other contexts. Most non-reserved key words are actually the names of built-in tables and functions specified by SQL. The concept of non-reserved key words essentially only exists to declare that some predefined meaning is attached to a word in some contexts.

In the PostgreSQL parser life is a bit more complicated. There are several different classes of tokens ranging from those that can never be used as an identifier to those that have absolutely no special status in the parser as compared to an ordinary identifier. (The latter is usually the case for functions specified by SQL.) Even reserved key words are not completely reserved in PostgreSQL, but can be used as column labels (for example, SELECT 55 AS CHECK, even though CHECK is a reserved key word).

In Table C.1 in the column for PostgreSQL we classify as “non-reserved” those key words that are explicitly known to the parser but are allowed as column or table names. Some key words that are otherwise non-reserved cannot be used as function or data type names and are marked accordingly. (Most of these words represent built-in functions or data types with special syntax. The function or type is still available but it cannot be redefined by the user.) Labeled “reserved” are those tokens that are not allowed as column or table names. Some reserved key words are allowable as names for functions or data types; this is also shown in the table. If not so marked, a reserved key word is only allowed as an “AS” column label name.

As a general rule, if you get spurious parser errors for commands that contain any of the listed key words as an identifier you should try to quote the identifier to see if the problem goes away.

It is important to understand before studying Table C.1 that the fact that a key word is not reserved in PostgreSQL does not mean that the feature related to the word is not implemented. Conversely, the presence of a key word does not indicate the existence of a feature.

Table C.1. SQL Key Words

Key Word	PostgreSQL	SQL:2011	SQL:2008	SQL-92
A		non-reserved	non-reserved
ABORT	non-reserved
ABS		reserved	reserved
ABSENT		non-reserved	non-reserved
ABSOLUTE	non-reserved	non-reserved	non-reserved	reserved
ACCESS	non-reserved
ACCORDING		non-reserved	non-reserved
ACTION	non-reserved	non-reserved	non-reserved	reserved
ADA		non-reserved	non-reserved	non-reserved
ADD	non-reserved	non-reserved	non-reserved	reserved
ADMIN	non-reserved	non-reserved	non-reserved
AFTER	non-reserved	non-reserved	non-reserved
AGGREGATE	non-reserved
ALL	reserved	reserved	reserved	reserved
ALLOCATE		reserved	reserved	reserved
ALSO	non-reserved
ALTER	non-reserved	reserved	reserved	reserved
ALWAYS	non-reserved	non-reserved	non-reserved
ANALYSE	reserved
ANALYZE	reserved
AND	reserved	reserved	reserved	reserved
ANY	reserved	reserved	reserved	reserved
ARE		reserved	reserved	reserved
ARRAY	reserved	reserved	reserved
ARRAY_AGG		reserved	reserved
ARRAY_MAX_CARDINALITY		reserved
AS	reserved	reserved	reserved	reserved
ASC	reserved	non-reserved	non-reserved	reserved
ASENSITIVE		reserved	reserved
ASSERTION	non-reserved	non-reserved	non-reserved	reserved
ASSIGNMENT	non-reserved	non-reserved	non-reserved
ASYMMETRIC	reserved	reserved	reserved
AT	non-reserved	reserved	reserved	reserved
ATOMIC		reserved	reserved
ATTACH	non-reserved
ATTRIBUTE	non-reserved	non-reserved	non-reserved
ATTRIBUTES		non-reserved	non-reserved
AUTHORIZATION	reserved (can be function or type)	reserved	reserved	reserved
AVG		reserved	reserved	reserved
BACKWARD	non-reserved
BASE64		non-reserved	non-reserved
BEFORE	non-reserved	non-reserved	non-reserved
BEGIN	non-reserved	reserved	reserved	reserved
BEGIN_FRAME		reserved
BEGIN_PARTITION		reserved
BERNOULLI		non-reserved	non-reserved
BETWEEN	non-reserved (cannot be function or type)	reserved	reserved	reserved
BIGINT	non-reserved (cannot be function or type)	reserved	reserved
BINARY	reserved (can be function or type)	reserved	reserved
BIT	non-reserved (cannot be function or type)			reserved
BIT_LENGTH				reserved
BLOB		reserved	reserved
BLOCKED		non-reserved	non-reserved
BOM		non-reserved	non-reserved
BOOLEAN	non-reserved (cannot be function or type)	reserved	reserved
BOTH	reserved	reserved	reserved	reserved
BREADTH		non-reserved	non-reserved
BY	non-reserved	reserved	reserved	reserved

C		non-reserved	non-reserved	non-reserved
CACHE	non-reserved
CALL		reserved	reserved
CALLED	non-reserved	reserved	reserved
CARDINALITY		reserved	reserved
CASCADE	non-reserved	non-reserved	non-reserved	reserved
CASCADED	non-reserved	reserved	reserved	reserved
CASE	reserved	reserved	reserved	reserved
CAST	reserved	reserved	reserved	reserved
CATALOG	non-reserved	non-reserved	non-reserved	reserved
CATALOG_NAME		non-reserved	non-reserved	non-reserved
CEIL		reserved	reserved
CEILING		reserved	reserved
CHAIN	non-reserved	non-reserved	non-reserved
CHAR	non-reserved (cannot be function or type)	reserved	reserved	reserved
CHARACTER	non-reserved (cannot be function or type)	reserved	reserved	reserved
CHARACTERISTICS	non-reserved	non-reserved	non-reserved
CHARACTERS		non-reserved	non-reserved
CHARACTER_LENGTH		reserved	reserved	reserved
CHARACTER_SET_CATALOG		non-reserved	non-reserved	non-reserved
CHARACTER_SET_NAME		non-reserved	non-reserved	non-reserved
CHARACTER_SET_SCHEMA		non-reserved	non-reserved	non-reserved
CHAR_LENGTH		reserved	reserved	reserved
CHECK	reserved	reserved	reserved	reserved
CHECKPOINT	non-reserved
CLASS	non-reserved
CLASS_ORIGIN		non-reserved	non-reserved	non-reserved
CLOB		reserved	reserved
CLOSE	non-reserved	reserved	reserved	reserved
CLUSTER	non-reserved
COALESCE	non-reserved (cannot be function or type)	reserved	reserved	reserved
COBOL		non-reserved	non-reserved	non-reserved
COLLATE	reserved	reserved	reserved	reserved
COLLATION	reserved (can be function or type)	non-reserved	non-reserved	reserved
COLLATION_CATALOG		non-reserved	non-reserved	non-reserved
COLLATION_NAME		non-reserved	non-reserved	non-reserved
COLLATION_SCHEMA		non-reserved	non-reserved	non-reserved
COLLECT		reserved	reserved
COLUMN	reserved	reserved	reserved	reserved
COLUMNS	non-reserved	non-reserved	non-reserved
COLUMN_NAME		non-reserved	non-reserved	non-reserved
COMMAND_FUNCTION		non-reserved	non-reserved	non-reserved
COMMAND_FUNCTION_CODE		non-reserved	non-reserved
COMMENT	non-reserved
COMMENTS	non-reserved
COMMIT	non-reserved	reserved	reserved	reserved
COMMITTED	non-reserved	non-reserved	non-reserved	non-reserved
CONCURRENTLY	reserved (can be function or type)
CONDITION		reserved	reserved
CONDITION_NUMBER		non-reserved	non-reserved	non-reserved
CONFIGURATION	non-reserved
CONFLICT	non-reserved
CONNECT		reserved	reserved	reserved
CONNECTION	non-reserved	non-reserved	non-reserved	reserved
CONNECTION_NAME		non-reserved	non-reserved	non-reserved
CONSTRAINT	reserved	reserved	reserved	reserved
CONSTRAINTS	non-reserved	non-reserved	non-reserved	reserved
CONSTRAINT_CATALOG		non-reserved	non-reserved	non-reserved
CONSTRAINT_NAME		non-reserved	non-reserved	non-reserved
CONSTRAINT_SCHEMA		non-reserved	non-reserved	non-reserved
CONSTRUCTOR		non-reserved	non-reserved
CONTAINS		reserved	non-reserved
CONTENT	non-reserved	non-reserved	non-reserved
CONTINUE	non-reserved	non-reserved	non-reserved	reserved
CONTROL		non-reserved	non-reserved
CONVERSION	non-reserved
CONVERT		reserved	reserved	reserved
COPY	non-reserved
CORR		reserved	reserved
CORRESPONDING		reserved	reserved	reserved
COST	non-reserved
COUNT		reserved	reserved	reserved
COVAR_POP		reserved	reserved
COVAR_SAMP		reserved	reserved
CREATE	reserved	reserved	reserved	reserved
CROSS	reserved (can be function or type)	reserved	reserved	reserved
CSV	non-reserved
CUBE	non-reserved	reserved	reserved
CUME_DIST		reserved	reserved
CURRENT	non-reserved	reserved	reserved	reserved
CURRENT_CATALOG	reserved	reserved	reserved
CURRENT_DATE	reserved	reserved	reserved	reserved
CURRENT_DEFAULT_TRANSFORM_GROUP		reserved	reserved
CURRENT_PATH		reserved	reserved
CURRENT_ROLE	reserved	reserved	reserved
CURRENT_ROW		reserved
CURRENT_SCHEMA	reserved (can be function or type)	reserved	reserved
CURRENT_TIME	reserved	reserved	reserved	reserved
CURRENT_TIMESTAMP	reserved	reserved	reserved	reserved
CURRENT_TRANSFORM_GROUP_FOR_TYPE		reserved	reserved
CURRENT_USER	reserved	reserved	reserved	reserved
CURSOR	non-reserved	reserved	reserved	reserved
CURSOR_NAME		non-reserved	non-reserved	non-reserved
CYCLE	non-reserved	reserved	reserved
DATA	non-reserved	non-reserved	non-reserved	non-reserved