[sharadgaur]

Summary

Allow the existing COMMENT, CODEC and TTL column modifiers in any order in CREATE TABLE, ALTER ADD COLUMN and ALTER MODIFY COLUMN.

The parser currently expects COMMENT before CODEC, but the formatter writes CODEC before COMMENT. A definition with both modifiers can parse successfully and then fail when its formatted output is parsed again.

CREATE TABLE db.example (
    event_time DateTime,
    value String CODEC(ZSTD(1)) COMMENT 'example'
) ENGINE = MergeTree ORDER BY event_time;

• Reuse the existing modifier parsers in a trailing-modifier loop.
• Reject duplicate COMMENT, CODEC and TTL clauses.
• Format in canonical COMMENT, CODEC, TTL order.
• Keep existing AST types and the preceding default/materialized/alias parsing unchanged.

Verification

• Full make test passes with Go 1.21.13 and Go 1.25.1, including race and compatibility tests. Go 1.21 used external linking for the local macOS linker requirement.
• Grouped tests cover all six modifier permutations across CREATE, ADD and MODIFY, mixed keyword casing, source end positions, compact/beautified round trips, duplicates and malformed clauses.
• Added generic SQL fixtures and regenerated AST/format goldens.
• make lint passes with golangci-lint 1.64.5. The CI-pinned 1.53.3 binary was not used locally.
• Full vet reports the existing Formatter.WriteByte signature warning, also reproduced on clean master. Other vet analyzers pass.

ClickHouse 26.8's column parser accepts these trailing modifiers in any order and rejects duplicates. Its formatter uses COMMENT, CODEC, TTL order.

Canonical output was also accepted by the available native ClickHouse 26.2.1.1089 formatter. Noncanonical input ordering was checked against the 26.8 source, not a running 26.8 binary; the older binary rejects that input ordering.