A "table factor" (name borrowed from the ANSI SQL grammar) is a table
name or a derived table (subquery), followed by an optional `AS` and an
optional alias. (The alias is *not* optional for subqueries, but we
don't enforce that.) It can appear in the FROM/JOIN part of the query.
This commit:
- introduces ASTNode::TableFactor
- changes the parser to populate SQLSelect::relation and Join::relation
with ASTNode::TableFactor instead of the table name
- changes the parser to only accept subqueries or identifiers, not
arbitrary expressions in the "table factor" context
- always parses the table name as SQLCompoundIdentifier (whether or not
it was actually compound).
i.e. ASC/DESC/unspecified - so that we don't lose information about
source code.
Also don't take any keyword other than ASC/DESC or Comma to mean
'ascending'.
...as this syntax is not specific to the PostgreSQL dialect.
Also use verified() to assert that parsing + serializing results in the
original SQL string.
Mainly by replacing `assert_eq!(sql, ast.to_string())` with a call to
the recently introduced `verified()` helper or using `parses_to()` where
the expected serialization differs from the original SQL string.
There was one case (parse_implicit_join), where the inputs were different:
let sql = "SELECT * FROM t1,t2";
//vs
let sql = "SELECT * FROM t1, t2";
and since we don't test the whitespace handling in other tests, I just
used the canonical representation as input.
