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[snowflake] Support specifying an alias after FROM (table_factor)

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Snowflake diverges from the standard and from most of the other
implementations by allowing extra parentheses not only around a join,
but around lone table names (e.g. `FROM (mytable [AS alias])`) and
around derived tables (e.g. `FROM ((SELECT ...)  [AS alias])`) as well.

Initially this was implemented in https://github.com/ballista-compute/sqlparser-rs/issues/154
by (ab)using `TableFactor::NestedJoin` to represent anything nested in
extra set of parens.

Afterwards we learned in https://github.com/ballista-compute/sqlparser-rs/issues/223
that in cases of such extraneous nesting Snowflake allows specifying the
alias both inside and outside parens, but not both - consider:

    FROM (table_factor AS inner_alias) AS outer_alias

We've considered implementing this by changing `TableFactor::NestedJoin`
to a `TableFactor::Nested { inner: TableWithJoins, alias:
Option<TableAlias> }`, but that seemed too generic, as no known dialect
supports duplicate aliases, as shown above, nor naming nested joins
`(foo NATURAL JOIN bar) alias`. So we decided on making a smaller change
(with no modifications to the AST), that is also more appropriate to the
contributors to the Snowflake dialect:


1) Revert #154 by rejecting `FROM (table or derived table)` in most dialects.

2) For `dialect_of!(self is SnowflakeDialect | GenericDialect)` parse
and strip the extraneous parentheses, e.g.

   `(mytable) AS alias` -> `(mytable AS alias)`


Co-authored-by: Eyal Leshem <eyal@satoricyber.com>
This commit is contained in:
Nickolay Ponomarev 2020-10-13 09:29:16 +03:00
parent d9e044aabb
commit ad72cda6b0
5 changed files with 131 additions and 46 deletions
Download patch file Download diff file Expand all files Collapse all files

7
src/ast/query.rs
View file

@ -242,9 +242,10 @@ pub enum TableFactor {
},
/// Represents a parenthesized table factor. The SQL spec only allows a
/// join expression (`(foo <JOIN> bar [ <JOIN> baz ... ])`) to be nested,
/// possibly several times, but the parser also accepts the non-standard
/// nesting of bare tables (`table_with_joins.joins.is_empty()`), so the
/// name `NestedJoin` is a bit of misnomer.
/// possibly several times.
///
/// The parser may also accept non-standard nesting of bare tables for some
/// dialects, but the information about such nesting is stripped from AST.
NestedJoin(Box<TableWithJoins>),
}

60
src/parser.rs
View file

@ -2156,14 +2156,58 @@ impl<'a> Parser<'a> {
// recently consumed does not start a derived table (cases 1, 2, or 4).
// `maybe_parse` will ignore such an error and rewind to be after the opening '('.
// 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)))
// Inside the parentheses we expect to find an (A) table factor
// followed by some joins or (B) another level of nesting.
let mut table_and_joins = self.parse_table_and_joins()?;
if !table_and_joins.joins.is_empty() {
self.expect_token(&Token::RParen)?;
Ok(TableFactor::NestedJoin(Box::new(table_and_joins))) // (A)
} else if let TableFactor::NestedJoin(_) = &table_and_joins.relation {
// (B): `table_and_joins` (what we found inside the parentheses)
// is a nested join `(foo JOIN bar)`, not followed by other joins.
self.expect_token(&Token::RParen)?;
Ok(TableFactor::NestedJoin(Box::new(table_and_joins)))
} else if dialect_of!(self is SnowflakeDialect | GenericDialect) {
// Dialect-specific behavior: Snowflake diverges from the
// standard and from most of the other implementations by
// allowing extra parentheses not only around a join (B), but
// around lone table names (e.g. `FROM (mytable [AS alias])`)
// and around derived tables (e.g. `FROM ((SELECT ...)
// [AS alias])`) as well.
self.expect_token(&Token::RParen)?;
if let Some(outer_alias) =
self.parse_optional_table_alias(keywords::RESERVED_FOR_TABLE_ALIAS)?
{
// Snowflake also allows specifying an alias *after* parens
// e.g. `FROM (mytable) AS alias`
match &mut table_and_joins.relation {
TableFactor::Derived { alias, .. }
| TableFactor::Table { alias, .. }
| TableFactor::TableFunction { alias, .. } => {
// but not `FROM (mytable AS alias1) AS alias2`.
if let Some(inner_alias) = alias {
return Err(ParserError::ParserError(format!(
"duplicate alias {}",
inner_alias
)));
}
// Act as if the alias was specified normally next
// to the table name: `(mytable) AS alias` ->
// `(mytable AS alias)`
alias.replace(outer_alias);
}
TableFactor::NestedJoin(_) => unreachable!(),
};
}
// Do not store the extra set of parens in the AST
Ok(table_and_joins.relation)
} else {
// The SQL spec prohibits derived tables and bare tables from
// appearing alone in parentheses (e.g. `FROM (mytable)`)
self.expected("joined table", self.peek_token())
}
} else {
let name = self.parse_object_name()?;
// Postgres, MSSQL: table-valued functions:

7
src/test_utils.rs
View file

@ -156,6 +156,13 @@ pub fn number(n: &'static str) -> Value {
Value::Number(n.parse().unwrap())
}
pub fn table_alias(name: impl Into<String>) -> Option<TableAlias> {
Some(TableAlias {
name: Ident::new(name),
columns: vec![],
})
}
pub fn table(name: impl Into<String>) -> TableFactor {
TableFactor::Table {
name: ObjectName(vec![Ident::new(name.into())]),

9
tests/sqlparser_common.rs
View file

@ -20,7 +20,7 @@
#[macro_use]
mod test_utils;
use test_utils::{all_dialects, expr_from_projection, join, number, only, table};
use test_utils::{all_dialects, expr_from_projection, join, number, only, table, table_alias};
use matches::assert_matches;
use sqlparser::ast::*;
@ -2130,13 +2130,6 @@ fn parse_cross_join() {
);
}
fn table_alias(name: impl Into<String>) -> Option<TableAlias> {
Some(TableAlias {
name: Ident::new(name),
columns: vec![],
})
}
#[test]
fn parse_joins_on() {
fn join_with_constraint(

94
tests/sqlparser_snowflake.rs
View file

@ -20,6 +20,7 @@ use test_utils::*;
use sqlparser::ast::*;
use sqlparser::dialect::{GenericDialect, SnowflakeDialect};
use sqlparser::parser::ParserError;
use sqlparser::tokenizer::*;
#[test]
@ -72,42 +73,81 @@ fn test_snowflake_single_line_tokenize() {
}
#[test]
fn test_sf_derives_single_table_in_parenthesis() {
// Nesting a subquery in parentheses is non-standard, but supported in Snowflake SQL
let sql = "SELECT * FROM ((SELECT 1) AS t)";
let select = snowflake_and_generic().verified_only_select(sql);
let from = only(select.from);
assert_eq!(
from.relation,
TableFactor::NestedJoin(Box::new(TableWithJoins {
relation: TableFactor::Derived {
lateral: false,
subquery: Box::new(snowflake_and_generic().verified_query("SELECT 1")),
alias: Some(TableAlias {
name: "t".into(),
columns: vec![],
})
},
joins: Vec::new(),
}))
fn test_sf_derived_table_in_parenthesis() {
// Nesting a subquery in an extra set of parentheses is non-standard,
// but supported in Snowflake SQL
snowflake_and_generic().one_statement_parses_to(
"SELECT * FROM ((SELECT 1) AS t)",
"SELECT * FROM (SELECT 1) AS t",
);
snowflake_and_generic().one_statement_parses_to(
"SELECT * FROM (((SELECT 1) AS t))",
"SELECT * FROM (SELECT 1) AS t",
);
}
#[test]
fn test_single_table_in_parenthesis() {
// Parenthesized table names are non-standard, but supported in Snowflake SQL
let sql = "SELECT * FROM (a NATURAL JOIN (b))";
let select = snowflake_and_generic().verified_only_select(sql);
let from = only(select.from);
snowflake_and_generic().one_statement_parses_to(
"SELECT * FROM (a NATURAL JOIN (b))",
"SELECT * FROM (a NATURAL JOIN b)",
);
snowflake_and_generic().one_statement_parses_to(
"SELECT * FROM (a NATURAL JOIN ((b)))",
"SELECT * FROM (a NATURAL JOIN b)",
);
}
assert_eq!(from.relation, nest!(table("a"), nest!(table("b"))));
#[test]
fn test_single_table_in_parenthesis_with_alias() {
snowflake_and_generic().one_statement_parses_to(
"SELECT * FROM (a NATURAL JOIN (b) c )",
"SELECT * FROM (a NATURAL JOIN b AS c)",
);
// Double parentheses around table names are non-standard, but supported in Snowflake SQL
let sql = "SELECT * FROM (a NATURAL JOIN ((b)))";
let select = snowflake_and_generic().verified_only_select(sql);
let from = only(select.from);
snowflake_and_generic().one_statement_parses_to(
"SELECT * FROM (a NATURAL JOIN ((b)) c )",
"SELECT * FROM (a NATURAL JOIN b AS c)",
);
assert_eq!(from.relation, nest!(table("a"), nest!(nest!(table("b")))));
snowflake_and_generic().one_statement_parses_to(
"SELECT * FROM (a NATURAL JOIN ( (b) c ) )",
"SELECT * FROM (a NATURAL JOIN b AS c)",
);
snowflake_and_generic().one_statement_parses_to(
"SELECT * FROM (a NATURAL JOIN ( (b) as c ) )",
"SELECT * FROM (a NATURAL JOIN b AS c)",
);
snowflake_and_generic().one_statement_parses_to(
"SELECT * FROM (a alias1 NATURAL JOIN ( (b) c ) )",
"SELECT * FROM (a AS alias1 NATURAL JOIN b AS c)",
);
snowflake_and_generic().one_statement_parses_to(
"SELECT * FROM (a as alias1 NATURAL JOIN ( (b) as c ) )",
"SELECT * FROM (a AS alias1 NATURAL JOIN b AS c)",
);
let res = snowflake_and_generic().parse_sql_statements("SELECT * FROM (a NATURAL JOIN b) c");
assert_eq!(
ParserError::ParserError("Expected end of statement, found: c".to_string()),
res.unwrap_err()
);
let res = snowflake().parse_sql_statements("SELECT * FROM (a b) c");
assert_eq!(
ParserError::ParserError("duplicate alias b".to_string()),
res.unwrap_err()
);
}
fn snowflake() -> TestedDialects {
TestedDialects {
dialects: vec![Box::new(SnowflakeDialect {})],
}
}
fn snowflake_and_generic() -> TestedDialects {