IBM Informix Keyword Compatibility Reference

Generated for GSP Java version 4.1.0.8 on 2026-03-15

This page was generated using hybrid static extraction from parser source files combined with runtime validation against the actual GSP parser. Re-run the extraction script after parser updates to keep this page current.

Keyword-as-Column-Name Support

As of version 4.1.0.8, the GSP IBM Informix parser includes a lexer lookahead mechanism that allows 15 vendor-unreserved keywords to be used as unquoted column names in SELECT statements.

The lookahead pre-scans the token list before parsing and converts context-specific keywords to identifiers when they appear in column-name position:

• After: SELECT, ,, DISTINCT, or ALL
• Before: FROM, AS, WHERE, GROUP, ORDER, HAVING, LIMIT, UNION, INTERSECT, EXCEPT, INTO, ,, ), or ;

-- Works: keyword as column name
SELECT case FROM t;

-- Works: keyword as column name
SELECT connect_by_root FROM t;

-- Works: keyword as column name
SELECT datetime FROM t;

-- Original keyword syntax also still works

---

Full Classification Overview

Out of 703 keywords recognized by the GSP IBM Informix parser:

Classification	Count	Description
Allowed	659	Can be used as an unquoted column name in both canonical contexts
Context-specific	17	Fails as SELECT keyword FROM t but works as SELECT t.keyword FROM t
Blocked	27	Cannot be used as an unquoted column name in either context

Context-Specific Keywords (17)

These keywords fail when used as bare column names (SELECT keyword FROM t) but succeed when table-qualified (SELECT t.keyword FROM t).

Keyword	Reason
ALL	SELECT qualifier
CASE	Expression keyword
CONNECT_BY_ROOT	Grammar keyword
DATETIME	Grammar keyword
DISTINCT	SELECT qualifier
EXTEND	Grammar keyword
FIRST	Grammar keyword
INTERVAL	Type keyword
LIMIT	Clause keyword
LIST	Grammar keyword
MULTISET	Grammar keyword
PRIOR	Grammar keyword
SET	Grammar keyword
SKIP	Grammar keyword
SUBSTRING	Expression keyword
UNION	Clause keyword
UNIQUE	Grammar keyword

Blocked Keywords (27)

These keywords cannot be used as unquoted column names in either context.

Keyword	Workaround
BEGIN	SELECT "begin" FROM t
CLOSE	SELECT "close" FROM t
COMMIT	SELECT "commit" FROM t
DECLARE	SELECT "declare" FROM t
DELETE	SELECT "delete" FROM t
DESCRIBE	SELECT "describe" FROM t
DISCONNECT	SELECT "disconnect" FROM t
EXEC	SELECT "exec" FROM t
EXECUTE	SELECT "execute" FROM t
FETCH	SELECT "fetch" FROM t
FLUSH	SELECT "flush" FROM t
FREE	SELECT "free" FROM t
FROM	SELECT "from" FROM t
GRANT	SELECT "grant" FROM t
INSERT	SELECT "insert" FROM t
LOAD	SELECT "load" FROM t
MERGE	SELECT "merge" FROM t
OPEN	SELECT "open" FROM t
OUTPUT	SELECT "output" FROM t
PREPARE	SELECT "prepare" FROM t
ROLLBACK	SELECT "rollback" FROM t
SAVEPOINT	SELECT "savepoint" FROM t
SELECT	SELECT "select" FROM t
TRUNCATE	SELECT "truncate" FROM t
UNLOAD	SELECT "unload" FROM t
UPDATE	SELECT "update" FROM t
WHENEVER	SELECT "whenever" FROM t

Workaround: Double-Quoted Identifiers

For any keyword that fails as an unquoted column name, you can use double-quoted identifiers:

-- Blocked or context-specific keyword as column name
SELECT "begin" FROM t;

-- Or use table qualification for context-specific keywords
SELECT t.all FROM t;

Scope and Limitations

• Tested contexts: SELECT keyword FROM t and SELECT t.keyword FROM t. Other contexts (DDL column definitions, INSERT column lists, aliases) may behave differently.
• Version-specific: This report reflects GSP Java version 4.1.0.8.
• Case sensitivity: Keywords are case-insensitive. select, SELECT, and Select are all treated the same.

How to Report Discrepancies

If you encounter a keyword that behaves differently from what this page describes, please report it through your support channel. Include:

1. The exact SQL statement
2. The GSP parser version
3. Whether the same SQL works in IBM Informix

Methodology

1. Static extraction: A Python script parses the lexer (.cod) and grammar (.y) source files to identify all 703 keywords and their grammar classifications.
2. Runtime validation: A Java test harness validates every classification against actual TGSqlParser runtime behavior.
3. JSON dataset: The authoritative data is stored in docs/generated/informix_keyword_compatibility.json.