C. SQL 關鍵字

Table C.1 列出了在 SQL 標準和 PostgreSQL 15.2 中作為關鍵字的所有標記。相關說明提供於第 4.1.1 節中。（由於篇幅原因，僅收錄了 SQL 標準的最新兩個版本，以及用於歷史對比的 SQL-92，與其他中間標準版本差異較小。）

SQL 區分保留(reserved)關鍵字和非保留(non-reserved)關鍵字。根據標準，只有保留關鍵字才是真正的關鍵字；他們永遠不允許作為標識字串。非保留關鍵字則只在特定的用法中有特殊的含義，而在其他用法中可以作為標識字串使用。大多數非保留關鍵字實際上是 SQL 指定的內建資料表和函數的名稱。非保留關鍵字的概念本質上只是為了聲明在某些用法中增加了一些預先定義的含義。

在 PostgreSQL 解析器中，情況有點複雜。有幾種不同類別的標記，從永遠不能用作標識字串的標記，到在解析器中絕對沒有特殊地位，但被視為普通標識字串的標記都有。（後者通常是 SQL 指定的函數。）即使保留關鍵字在 PostgreSQL 中也沒有完全保留，而是可以用作欄位標籤（例如 SELECT 55 AS CHECK 是可以的，儘管 CHECK 是保留關鍵字） .

在 Table C.1 的 PostgreSQL 欄位中，我們將解析器明確知道但允許作為欄位名稱或資料表名稱的那些關鍵字分類為“non-reserved”。一些非保留的關鍵字不能用作函數或資料型別名稱，並相應地進行標記。（這些詞大多表示具有特殊語法的內建函數或資料型別。函數或型別仍然可用，但使用者不能重新定義。）標記為“reserved”的是那些不允許作為欄位或資料表名稱的標記。允許一些保留關鍵字作為函數或資料型別的名稱；這也顯示在表格中。如果沒有這樣標記，保留關鍵字僅允許作為欄位標籤。此欄中的空白項目表示該關鍵字被 PostgreSQL 視為普通標識字串。

此外，雖然大多數關鍵字可以直接用作欄位標籤而毋須在它們之前使用 AS（如第 7.3.2 節所述），但有一些關鍵詞需要前導 AS 以避免歧義。在下表中這些關鍵字會標記為“requires AS”。

一般來說，如果使用任何列出的關鍵字作為標識字的命令出現解析錯誤的時候，您應該嘗試將標識字以雙引號括住，再查看問題是否消失。

在研究 Table C.1 之前，重要的是要了解，在 PostgreSQL 中沒有保留關鍵字並不意味著沒有實作與該關鍵字相關的功能。同樣地，關鍵字的存在也不表示其功能的存在。

Table C.1. SQL Key Words

Key Word

PostgreSQL

SQL:2016

SQL:2011

SQL-92

A

non-reserved

ABORT

non-reserved

ABS

reserved

ABSENT

reserved

non-reserved

ABSOLUTE

non-reserved

reserved

ACCESS

non-reserved

ACCORDING

non-reserved

ACOS

reserved

ACTION

non-reserved

reserved

ADA

non-reserved

ADD

non-reserved

reserved

ADMIN

non-reserved

AFTER

non-reserved

AGGREGATE

non-reserved

ALL

reserved

ALLOCATE

reserved

ALSO

non-reserved

ALTER

non-reserved

reserved

ALWAYS

non-reserved

ANALYSE

reserved

ANALYZE

reserved

AND

reserved

ANY

reserved

ARE

reserved

ARRAY

reserved, requires AS

reserved

ARRAY_AGG

reserved

ARRAY_MAX_CARDINALITY

reserved

AS

reserved, requires AS

reserved

ASC

reserved

non-reserved

reserved

ASENSITIVE

non-reserved

reserved

ASIN

reserved

ASSERTION

non-reserved

reserved

ASSIGNMENT

non-reserved

ASYMMETRIC

reserved

AT

non-reserved

reserved

ATAN

reserved

ATOMIC

non-reserved

reserved

ATTACH

non-reserved

ATTRIBUTE

non-reserved

ATTRIBUTES

non-reserved

AUTHORIZATION

reserved (can be function or type)

reserved

AVG

reserved

BACKWARD

non-reserved

BASE64

non-reserved

BEFORE

non-reserved

BEGIN

non-reserved

reserved

BEGIN_FRAME

reserved

BEGIN_PARTITION

reserved

BERNOULLI

non-reserved

BETWEEN

non-reserved (cannot be function or type)

reserved

BIGINT

non-reserved (cannot be function or type)

reserved

BINARY

reserved (can be function or type)

reserved

BIT

non-reserved (cannot be function or type)

reserved

BIT_LENGTH

reserved

BLOB

reserved

BLOCKED

non-reserved

BOM

non-reserved

BOOLEAN

non-reserved (cannot be function or type)

reserved

BOTH

reserved

BREADTH

non-reserved

BY

non-reserved

reserved

C

non-reserved

CACHE

non-reserved

CALL

non-reserved

reserved

CALLED

non-reserved

reserved

CARDINALITY

reserved

CASCADE

non-reserved

reserved

CASCADED

non-reserved

reserved

CASE

reserved

CAST

reserved

CATALOG

non-reserved

reserved

CATALOG_NAME

non-reserved

CEIL

reserved

CEILING

reserved

CHAIN

non-reserved

CHAINING

non-reserved

CHAR

non-reserved (cannot be function or type), requires AS

reserved

CHARACTER

non-reserved (cannot be function or type), requires AS

reserved

CHARACTERISTICS

non-reserved

CHARACTERS

non-reserved

CHARACTER_LENGTH

reserved

CHARACTER_SET_CATALOG

non-reserved

CHARACTER_SET_NAME

non-reserved

CHARACTER_SET_SCHEMA

non-reserved

CHAR_LENGTH

reserved

CHECK

reserved

CHECKPOINT

non-reserved

CLASS

non-reserved

CLASSIFIER

reserved

CLASS_ORIGIN

non-reserved

CLOB

reserved

CLOSE

non-reserved

reserved

CLUSTER

non-reserved

COALESCE

non-reserved (cannot be function or type)

reserved

COBOL

non-reserved

COLLATE

reserved

COLLATION

reserved (can be function or type)

non-reserved

reserved

COLLATION_CATALOG

non-reserved

COLLATION_NAME

non-reserved

COLLATION_SCHEMA

non-reserved

COLLECT

reserved

COLUMN

reserved

COLUMNS

non-reserved

COLUMN_NAME

non-reserved

COMMAND_FUNCTION

non-reserved

COMMAND_FUNCTION_CODE

non-reserved

COMMENT

non-reserved

COMMENTS

non-reserved

COMMIT

non-reserved

reserved

COMMITTED

non-reserved

COMPRESSION

non-reserved

CONCURRENTLY

reserved (can be function or type)

CONDITION

reserved

CONDITIONAL

non-reserved

CONDITION_NUMBER

non-reserved

CONFIGURATION

non-reserved

CONFLICT

non-reserved

CONNECT

reserved

CONNECTION

non-reserved

reserved

CONNECTION_NAME

non-reserved

CONSTRAINT

reserved

CONSTRAINTS

non-reserved

reserved

CONSTRAINT_CATALOG

non-reserved

CONSTRAINT_NAME

non-reserved

CONSTRAINT_SCHEMA

non-reserved

CONSTRUCTOR

non-reserved

CONTAINS

reserved

CONTENT

non-reserved

CONTINUE

non-reserved

reserved

CONTROL

non-reserved

CONVERSION

non-reserved

CONVERT

reserved

COPY

non-reserved

reserved

CORR

reserved

CORRESPONDING

reserved

COS

reserved

COSH

reserved

COST

non-reserved

COUNT

reserved

COVAR_POP

reserved

COVAR_SAMP

reserved

CREATE

reserved, requires AS

reserved

CROSS

reserved (can be function or type)

reserved

CSV

non-reserved

CUBE

non-reserved

reserved

CUME_DIST

reserved

CURRENT

non-reserved

reserved

CURRENT_CATALOG

reserved

CURRENT_DATE

reserved

CURRENT_DEFAULT_TRANSFORM_GROUP

reserved

CURRENT_PATH

reserved

CURRENT_ROLE

reserved

CURRENT_ROW

reserved

CURRENT_SCHEMA

reserved (can be function or type)

reserved

CURRENT_TIME

reserved

CURRENT_TIMESTAMP

reserved

CURRENT_TRANSFORM_GROUP_FOR_TYPE

reserved

CURRENT_USER

reserved

CURSOR

non-reserved

reserved

CURSOR_NAME

non-reserved

CYCLE

non-reserved

reserved

DATA

non-reserved

DATABASE

non-reserved

DATALINK

reserved

DATE

reserved

DATETIME_INTERVAL_CODE

non-reserved

DATETIME_INTERVAL_PRECISION