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Update comments (follow-up to PR #155)

Browse source 
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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9
src/ast/query.rs
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@ -225,10 +225,11 @@ pub enum TableFactor {
subquery: Box<Query>, subquery: Box<Query>,
alias: Option<TableAlias>, alias: Option<TableAlias>,
}, },
/// Represents a parenthesized join expression, such as /// Represents a parenthesized table factor. The SQL spec only allows a
/// `(foo <JOIN> bar [ <JOIN> baz ... ])`. /// join expression (`(foo <JOIN> bar [ <JOIN> baz ... ])`) to be nested,
/// The inner `TableWithJoins` can have no joins only if its /// possibly several times, but the parser also accepts the non-standard
/// `relation` is itself a `TableFactor::NestedJoin`. /// nesting of bare tables (`table_with_joins.joins.is_empty()`), so the
/// name `NestedJoin` is a bit of misnomer.
NestedJoin(Box<TableWithJoins>), NestedJoin(Box<TableWithJoins>),
} }

26
src/parser.rs
View file

@ -1771,7 +1771,6 @@ impl Parser {
// ^ ^ ^ ^ // ^ ^ ^ ^
// | | | | // | | | |
// | | | | // | | | |
// | | | |
// | | | (4) belongs to a SetExpr::Query inside the subquery // | | | (4) belongs to a SetExpr::Query inside the subquery
// | | (3) starts a derived table (subquery) // | | (3) starts a derived table (subquery)
// | (2) starts a nested join // | (2) starts a nested join
@ -1784,23 +1783,20 @@ impl Parser {
// case (3), and the next token would be `NATURAL`. // case (3), and the next token would be `NATURAL`.
Ok(table_factor) => Ok(table_factor), Ok(table_factor) => Ok(table_factor),
Err(_) => { Err(_) => {
// The '(' we've recently consumed does not start a derived // A parsing error from `parse_derived_table_factor` indicates that
// table. For valid input this can happen either when the // the '(' we've recently consumed does not start a derived table
// token following the paren can't start a query (e.g. `foo` // (cases 1, 2, or 4). Ignore the error and back up to where we
// in `FROM (foo NATURAL JOIN bar)`, or when the '(' we've // were before - right after the opening '('.
// 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)
self.index = index; 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()?; let table_and_joins = self.parse_table_and_joins()?;
self.expect_token(&Token::RParen)?; 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))) Ok(TableFactor::NestedJoin(Box::new(table_and_joins)))
} }
} }