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Update comments (follow-up to PR #155)

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https://github.com/andygrove/sqlparser-rs/pull/155
This commit is contained in:
Nickolay Ponomarev 2020-04-20 04:07:21 +03:00
parent 33303b244f
commit 05a29212ff
2 changed files with 16 additions and 19 deletions
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26
src/parser.rs
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@ -1771,7 +1771,6 @@ impl Parser {
// ^ ^ ^ ^
// | | | |
// | | | |
// | | | |
// | | | (4) belongs to a SetExpr::Query inside the subquery
// | | (3) starts a derived table (subquery)
// | (2) starts a nested join
@ -1784,23 +1783,20 @@ impl Parser {
// case (3), and the next token would be `NATURAL`.
Ok(table_factor) => Ok(table_factor),
Err(_) => {
// The '(' we've recently consumed does not start a derived
// table. For valid input this can happen either when the
// token following the paren can't start a query (e.g. `foo`
// in `FROM (foo NATURAL JOIN bar)`, or when the '(' we've
// consumed is followed by another '(' that starts a
// derived table, like (3), or another nested join (2).
//
// Ignore the error and back up to where we were before.
// Either we'll be able to parse a valid nested join, or
// we won't, and we'll return that error instead.
//
// Even the SQL spec prohibits derived tables and bare
// tables from appearing alone in parentheses, we allowed it
// as some Db's allowed that (snowflake as example)
// A parsing error from `parse_derived_table_factor` indicates that
// the '(' we've recently consumed does not start a derived table
// (cases 1, 2, or 4). Ignore the error and back up to where we
// were before - right after the opening '('.
self.index = index;
// Inside the parentheses we expect to find a table factor
// followed by some joins or another level of nesting.
let table_and_joins = self.parse_table_and_joins()?;
self.expect_token(&Token::RParen)?;
// The SQL spec prohibits derived and bare tables from appearing
// alone in parentheses. We don't enforce this as some databases
// (e.g. Snowflake) allow such syntax.
Ok(TableFactor::NestedJoin(Box::new(table_and_joins)))
}
}