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IBM DB2 Keyword Compatibility Reference

Generated for GSP Java version 4.1.9 on 2026-07-29

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 DB2 parser includes a lexer lookahead mechanism that allows 23 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 ;
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-- Works: keyword as column name
SELECT array FROM t;

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

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

-- Original keyword syntax also still works

Full Classification Overview

Out of 573 keywords recognized by the GSP IBM DB2 parser:

Classification Count Description
Allowed 570 Can be used as an unquoted column name in both canonical contexts
Context-specific 2 Fails as SELECT keyword FROM t but works as SELECT t.keyword FROM t
Blocked 1 Cannot be used as an unquoted column name in either context

Context-Specific Keywords (2)

These keywords parse in one canonical context but not the other (measured against the release stamped above).

Keyword SELECT kw FROM t SELECT t.kw FROM t
ALL no yes
DISTINCT no yes

Blocked Keywords (1)

These keywords fail as unquoted identifiers in both canonical contexts. Workaround: quote the identifier (e.g. "KEYWORD").

Keyword
FROM

Workaround: Double-Quoted Identifiers

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

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-- Blocked or context-specific keyword as column name
SELECT "from" 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 DB2

Methodology

  1. Static extraction: A Python script parses the lexer (.cod) and grammar (.y) source files to identify all 573 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/db2_keyword_compatibility.json.