Use dialects in the parser for support snowflake aliasing syntax

src/ast/query.rs

@@ -235,11 +235,11 @@ pub enum TableFactor {
         subquery: Box<Query>,
         alias: Option<TableAlias>,
     },
-    /// 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.
+    /// The inner `TableWithJoins` can have no joins only if its
+    /// `relation` is itself a `TableFactor::NestedJoin`.
+    /// Some dialects allow nesting lone `Table`/`Derived` in parens,
+    /// e.g. `FROM (mytable)`, but we don't expose the presence of these
+    /// extraneous parens in the AST.
     NestedJoin(Box<TableWithJoins>),
 }
 

src/dialect/mod.rs

@@ -16,14 +16,15 @@ pub mod keywords;
 mod mssql;
 mod mysql;
 mod postgresql;
-
+mod snowflake;
 use std::fmt::Debug;
 
 pub use self::ansi::AnsiDialect;
 pub use self::generic::GenericDialect;
 pub use self::mssql::MsSqlDialect;
 pub use self::mysql::MySqlDialect;
 pub use self::postgresql::PostgreSqlDialect;
+pub use self::snowflake::SnowflakeDialect;
 
 pub trait Dialect: Debug {
     /// Determine if a character starts a quoted identifier. The default
@@ -38,4 +39,8 @@ pub trait Dialect: Debug {
     fn is_identifier_start(&self, ch: char) -> bool;
     /// Determine if a character is a valid unquoted identifier character
     fn is_identifier_part(&self, ch: char) -> bool;
+
+    fn alllow_single_table_in_parenthesis(&self) -> bool {
+        false
+    }
 }

src/dialect/snowflake.rs

@@ -0,0 +1,26 @@
+use crate::dialect::Dialect;
+
+#[derive(Debug, Default)]
+pub struct SnowflakeDialect;
+
+impl Dialect for SnowflakeDialect {
+    //Revisit: currently copied from Genric dialect
+    fn is_identifier_start(&self, ch: char) -> bool {
+        (ch >= 'a' && ch <= 'z') || (ch >= 'A' && ch <= 'Z') || ch == '_' || ch == '#' || ch == '@'
+    }
+
+    //Revisit: currently copied from Genric dialect
+    fn is_identifier_part(&self, ch: char) -> bool {
+        (ch >= 'a' && ch <= 'z')
+            || (ch >= 'A' && ch <= 'Z')
+            || (ch >= '0' && ch <= '9')
+            || ch == '@'
+            || ch == '$'
+            || ch == '#'
+            || ch == '_'
+    }
+
+    fn alllow_single_table_in_parenthesis(&self) -> bool {
+        true
+    }
+}

src/parser.rs

@@ -83,23 +83,28 @@ impl fmt::Display for ParserError {
 impl Error for ParserError {}
 
 /// SQL Parser
-pub struct Parser {
+pub struct Parser<'a> {
     tokens: Vec<Token>,
     /// The index of the first unprocessed token in `self.tokens`
     index: usize,
+    dialect: &'a dyn Dialect,
 }
 
-impl Parser {
+impl<'a> Parser<'a> {
     /// Parse the specified tokens
-    pub fn new(tokens: Vec<Token>) -> Self {
-        Parser { tokens, index: 0 }
+    pub fn new(tokens: Vec<Token>, dialect: &'a dyn Dialect) -> Self {
+        Parser {
+            tokens,
+            index: 0,
+            dialect,
+        }
     }
 
     /// Parse a SQL statement and produce an Abstract Syntax Tree (AST)
     pub fn parse_sql(dialect: &dyn Dialect, sql: &str) -> Result<Vec<Statement>, ParserError> {
         let mut tokenizer = Tokenizer::new(dialect, &sql);
         let tokens = tokenizer.tokenize()?;
-        let mut parser = Parser::new(tokens);
+        let mut parser = Parser::new(tokens, dialect);
         let mut stmts = Vec::new();
         let mut expecting_statement_delimiter = false;
         debug!("Parsing sql '{}'...", sql);
@@ -950,7 +955,7 @@ impl Parser {
     /// Parse a comma-separated list of 1+ items accepted by `F`
     pub fn parse_comma_separated<T, F>(&mut self, mut f: F) -> Result<Vec<T>, ParserError>
     where
-        F: FnMut(&mut Parser) -> Result<T, ParserError>,
+        F: FnMut(&mut Parser<'a>) -> Result<T, ParserError>,
     {
         let mut values = vec![];
         loop {
@@ -2056,6 +2061,7 @@ impl Parser {
             };
             joins.push(join);
         }
+
         Ok(TableWithJoins { relation, joins })
     }
 
@@ -2098,14 +2104,56 @@ impl Parser {
             // 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 self.dialect.alllow_single_table_in_parenthesis() {
+                // Dialect-specific behavior: Snowflake diverges from the
+                // standard and most of 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, .. } => {
+                            // 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:

src/test_utils.rs

@@ -53,7 +53,7 @@ impl TestedDialects {
         self.one_of_identical_results(|dialect| {
             let mut tokenizer = Tokenizer::new(dialect, sql);
             let tokens = tokenizer.tokenize().unwrap();
-            f(&mut Parser::new(tokens))
+            f(&mut Parser::new(tokens, dialect))
         })
     }
 
@@ -104,7 +104,9 @@ impl TestedDialects {
     /// Ensures that `sql` parses as an expression, and is not modified
     /// after a serialization round-trip.
     pub fn verified_expr(&self, sql: &str) -> Expr {
-        let ast = self.run_parser_method(sql, Parser::parse_expr).unwrap();
+        let ast = self
+            .run_parser_method(sql, |parser| parser.parse_expr())
+            .unwrap();
         assert_eq!(sql, &ast.to_string(), "round-tripping without changes");
         ast
     }

tests/sqlparser_common.rs

@@ -22,7 +22,7 @@ use matches::assert_matches;
 
 use sqlparser::ast::*;
 use sqlparser::dialect::keywords::ALL_KEYWORDS;
-use sqlparser::parser::{Parser, ParserError};
+use sqlparser::parser::ParserError;
 use sqlparser::test_utils::{all_dialects, expr_from_projection, number, only};
 
 #[test]
@@ -147,13 +147,14 @@ fn parse_update() {
 
 #[test]
 fn parse_invalid_table_name() {
-    let ast = all_dialects().run_parser_method("db.public..customer", Parser::parse_object_name);
+    let ast = all_dialects()
+        .run_parser_method("db.public..customer", |parser| parser.parse_object_name());
     assert!(ast.is_err());
 }
 
 #[test]
 fn parse_no_table_name() {
-    let ast = all_dialects().run_parser_method("", Parser::parse_object_name);
+    let ast = all_dialects().run_parser_method("", |parser| parser.parse_object_name());
     assert!(ast.is_err());
 }
 
@@ -2273,19 +2274,12 @@ fn parse_join_nesting() {
         vec![join(nest!(nest!(nest!(table("b"), table("c")))))]
     );
 
-    // Parenthesized table names are non-standard, but supported in Snowflake SQL
-    let sql = "SELECT * FROM (a NATURAL JOIN (b))";
-    let select = verified_only_select(sql);
-    let from = only(select.from);
-
-    assert_eq!(from.relation, nest!(table("a"), nest!(table("b"))));
-
-    // Double parentheses around table names are non-standard, but supported in Snowflake SQL
-    let sql = "SELECT * FROM (a NATURAL JOIN ((b)))";
-    let select = verified_only_select(sql);
-    let from = only(select.from);
-
-    assert_eq!(from.relation, nest!(table("a"), nest!(nest!(table("b")))));
+    // Nesting a subquery in parentheses is non-standard, but supported in Snowflake SQL
+    let res = parse_sql_statements("SELECT * FROM ((SELECT 1) AS t)");
+    assert_eq!(
+        ParserError::ParserError("Expected joined table, found: )".to_string()),
+        res.unwrap_err()
+    );
 }
 
 #[test]
@@ -2427,26 +2421,6 @@ fn parse_derived_tables() {
             }],
         }))
     );
-
-    // Nesting a subquery in parentheses is non-standard, but supported in Snowflake SQL
-    let sql = "SELECT * FROM ((SELECT 1) AS t)";
-    let select = 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(verified_query("SELECT 1")),
-                alias: Some(TableAlias {
-                    name: "t".into(),
-                    columns: vec![],
-                })
-            },
-            joins: Vec::new(),
-        }))
-    );
 }
 
 #[test]