The Ident type was previously an alias for a String. Turn it into a full
fledged struct, so that the parser can preserve the distinction between
identifier value and quote style already made by the tokenizer's Word
structure.
The SQL standard requires that numeric literals with a decimal point,
like 1.23, are represented exactly, up to some precision. That means
that parsing these literals into f64s is invalid, as it is impossible
to represent many decimal numbers exactly in binary floating point (for
example, 0.3).
This commit parses all numeric literals into a new `Value` variant
`Number(String)`, removing the old `Long(u64)` and `Double(f64)`
variants. This is slightly less convenient for downstream consumers, but
far more flexible, as numbers that do not fit into a u64 and f64 are now
representable.
The note about WindowFrameBound::Following being only valid "in
WindowFrame::end_bound" was both
- confusing, as it was based on the ANSI SQL syntax the parser doesn't
adhere to -- though it sounded like a promise about the AST one could
expect to get from the parser
- and incomplete, as the reality is that the bounds validation the SQL
engine might want to perform is more complex. For example Postgres
documentation says <https://www.postgresql.org/docs/11/sql-expressions.html#SYNTAX-WINDOW-FUNCTIONS>:
> Restrictions are that frame_start cannot be UNBOUNDED FOLLOWING,
> frame_end cannot be UNBOUNDED PRECEDING, and the frame_end choice
> cannot appear earlier in the above list of frame_start and frame_end
> options than the frame_start choice does — for example RANGE BETWEEN
> CURRENT ROW AND offset PRECEDING is not allowed. But, for example,
> ROWS BETWEEN 7 PRECEDING AND 8 PRECEDING is allowed, even though it
> would never select any rows.
It used to consume the `RParen` closing the encompassing `OVER (`, even
when no window frame was parsed, which confused me a bit, even though
I wrote it initially.
After fixing that, I took the opportunity to reduce nesting and
duplication a bit.
To use the new helper effectively, a few related changes were required:
- Each of the parse_..._list functions (`parse_cte_list`,
`parse_order_by_expr_list`, `parse_select_list`) was replaced with a
version that parses a single element of the list (e.g. `parse_cte`),
with their callers now using
`self.parse_comma_separated(Parser::parse_<one_element>)?`
- `parse_with_options` now parses the WITH keyword and a separate
`parse_sql_option` function (named after the struct it produces) was
added to parse a single k=v option.
- `parse_list_of_ids` is gone, with the '.'-separated parsing moved to
`parse_object_name`.
Custom comma-separated parsing is still used in:
- parse_transaction_modes (where the comma separator is optional)
- parse_columns (allows optional trailing comma, before the closing ')')
Remove outdated bits that claim shoddy SQL support and code
structure--we're much better on those fronts now! Also add a few
paragraphs about the current state of SQL compliance, why it's hard to
say anything detailed about SQL compliance, and what our long-term goals
are.
