alrevuelta opened a new pull request, #2333:
URL: https://github.com/apache/datafusion-sqlparser-rs/pull/2333
Fixes #2221.
ClickHouse's `WITH` clause supports a reversed-order form `<expression> AS
<identifier>` (alongside, and freely interleaved with, traditional CTEs).
Currently the parser hard-errors on the leading non-identifier token:
```
WITH 42 AS answer SELECT answer FROM t
-- Expected: identifier, found: 42
```
## Changes
- New `WithItem` enum (`Cte(Cte)` | `Named { expr, alias }`);
`With::cte_tables: Vec<Cte>` becomes `With::items: Vec<WithItem>`.
- New dialect flag `Dialect::supports_with_clause_scalar_expression`
(default `false`, `true` for `ClickHouseDialect` only).
- New `parse_with_item` routes each WITH-list element: when the leading
token can't begin a CTE name, it parses `<expr> AS <ident>` directly; otherwise
it tries the CTE form via `maybe_parse` and falls back. `parse_cte` itself is
unchanged.
## Tests
Added in `tests/sqlparser_clickhouse.rs`, covering: literal scalar (the
issue's example), string literal, aggregate, scalar subquery, bare-identifier
disambiguation, mixing scalar + CTE in one list, lambda, and a negative test
confirming non-ClickHouse dialects still reject the form.
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