The following terms have a special meaning in Firebird 2.5 DSQL. Some of them are also reserved words, others aren't.
!<
^<
^=
^>
,
:=
!=
!>
(
)
<
⇐
<>
=
>
>=
||
~<
~=
~>
ABS
ACCENT
ACOS
ACTION
ACTIVE
ADD
ADMIN
AFTER
ALL
ALTER
ALWAYS
AND
ANY
AS
ASC
ASCENDING
-
-
ASIN
AT
ATAN
ATAN2
AUTO
AUTONOMOUS
AVG
BACKUP
BEFORE
BEGIN
BETWEEN
BIGINT
BIN_AND
BIN_NOT
BIN_OR
BIN_SHL
BIN_SHR
BIN_XOR
BIT_LENGTH
BLOB
BLOCK
BOTH
BREAK
BY
CALLER
CASCADE
CASE
CAST
CEIL
CEILING
CHAR
CHAR_LENGTH
CHAR_TO_UUID
CHARACTER
CHARACTER_LENGTH
CHECK
CLOSE
COALESCE
COLLATE
COLLATION
COLUMN
COMMENT
COMMIT
COMMITTED
COMMON
COMPUTED
CONDITIONAL
CONNECT
CONSTRAINT
CONTAINING
COS
COSH
COT
COUNT
CREATE
CROSS
CSTRING
CURRENT
CURRENT_CONNECTION
CURRENT_DATE
CURRENT_ROLE
CURRENT_TIME
CURRENT_TIMESTAMP
CURRENT_TRANSACTION
CURRENT_USER
CURSOR
DATA
DATABASE
DATE
DATEADD
DATEDIFF
DAY
DEC
DECIMAL
DECLARE
DECODE
DEFAULT
DELETE
DELETING
DESC
DESCENDING
DESCRIPTOR
DIFFERENCE
DISCONNECT
DISTINCT
DO
DOMAIN
DOUBLE
DROP
ELSE
END
ENTRY_POINT
ESCAPE
EXCEPTION
EXECUTE
EXISTS
EXIT
EXP
EXTERNAL
EXTRACT
FETCH
FILE
FILTER
FIRST
FIRSTNAME
FLOAT
FLOOR
FOR
FOREIGN
FREE_IT
FROM
FULL
FUNCTION
GDSCODE
GEN_ID
GEN_UUID
GENERATED
GENERATOR
GLOBAL
GRANT
GRANTED
GROUP
HASH
HAVING
HOUR
IF
IGNORE
IIF
IN
INACTIVE
INDEX
INNER
INPUT_TYPE
INSENSITIVE
INSERT
INSERTING
INT
INTEGER
INTO
IS
ISOLATION
JOIN
KEY
LAST
LASTNAME
LEADING
LEAVE
LEFT
LENGTH
LEVEL
LIKE
LIMBO
LIST
LN
LOCK
LOG
LOG10
LONG
LOWER
LPAD
MANUAL
MAPPING
MATCHED
MATCHING
MAX
MAXIMUM_SEGMENT
MAXVALUE
MERGE
MIDDLENAME
MILLISECOND
MIN
MINUTE
MINVALUE
MOD
MODULE_NAME
MONTH
NAMES
NATIONAL
NATURAL
NCHAR
NEXT
NO
NOT
NULL
NULLIF
NULLS
NUMERIC
OCTET_LENGTH
OF
ON
ONLY
OPEN
OPTION
OR
ORDER
-
OUTER
OUTPUT_TYPE
OVERFLOW
OVERLAY
PAD
PAGE
PAGE_SIZE
PAGES
PARAMETER
PASSWORD
PI
PLACING
PLAN
POSITION
POST_EVENT
POWER
PRECISION
PRESERVE
PRIMARY
PRIVILEGES
PROCEDURE
PROTECTED
RAND
RDB$DB_KEY
READ
REAL
RECORD_VERSION
RECREATE
RECURSIVE
REFERENCES
RELEASE
REPLACE
REQUESTS
RESERV
RESERVING
RESTART
RESTRICT
RETAIN
RETURNING
RETURNING_VALUES
RETURNS
REVERSE
REVOKE
RIGHT
ROLE
ROLLBACK
ROUND
ROW_COUNT
ROWS
RPAD
SAVEPOINT
SCALAR_ARRAY
SCHEMA
SECOND
SEGMENT
SELECT
SENSITIVE
SEQUENCE
SET
SHADOW
SHARED
SIGN
SIMILAR
SIN
SINGULAR
SINH
SIZE
SKIP
SMALLINT
SNAPSHOT
SOME
SORT
SOURCE
SPACE
SQLCODE
SQLSTATE (2.5.1)
SQRT
STABILITY
START
STARTING
STARTS
STATEMENT
STATISTICS
SUB_TYPE
SUBSTRING
SUM
SUSPEND
TABLE
TAN
TANH
TEMPORARY
THEN
TIME
TIMEOUT
TIMESTAMP
TO
TRAILING
TRANSACTION
TRIGGER
TRIM
TRUNC
TWO_PHASE
TYPE
UNCOMMITTED
UNDO
UNION
UNIQUE
UPDATE
UPDATING
UPPER
USER
USING
UUID_TO_CHAR
VALUE
VALUES
VARCHAR
VARIABLE
VARYING
VIEW
WAIT
WEEK
WEEKDAY
WHEN
WHERE
WHILE
WITH
WORK
WRITE
YEAR
YEARDAY