Move TableFactor to be a separate enum

ASTNode can now be renamed SQLExpression, as it represents a node in
the "expression" part of the AST -- other nodes have their own types.

src/sqlast/mod.rs

@@ -20,7 +20,7 @@ mod sqltype;
 mod table_key;
 mod value;
 
-pub use self::query::{Join, JoinConstraint, JoinOperator, SQLOrderByExpr, SQLSelect};
+pub use self::query::{Join, JoinConstraint, JoinOperator, SQLOrderByExpr, SQLSelect, TableFactor};
 pub use self::sqltype::SQLType;
 pub use self::table_key::{AlterOperation, Key, TableKey};
 pub use self::value::Value;
@@ -30,7 +30,8 @@ pub use self::sql_operator::SQLOperator;
 /// Identifier name, in the originally quoted form (e.g. `"id"`)
 pub type SQLIdent = String;
 
-/// SQL Abstract Syntax Tree (AST)
+/// Represents a parsed SQL expression, which is a common building
+/// block of SQL statements (the part after SELECT, WHERE, etc.)
 #[derive(Debug, Clone, PartialEq)]
 pub enum ASTNode {
     /// Identifier e.g. table name or column name
@@ -73,11 +74,6 @@ pub enum ASTNode {
         results: Vec<ASTNode>,
         else_result: Option<Box<ASTNode>>,
     },
-    /// A table name or a parenthesized subquery with an optional alias
-    TableFactor {
-        relation: Box<ASTNode>, // SQLNested or SQLCompoundIdentifier
-        alias: Option<SQLIdent>,
-    },
     /// A parenthesized subquery `(SELECT ...)`, used in expression like
     /// `SELECT (subquery) AS x` or `WHERE (subquery) = x`
     SQLSubquery(SQLSelect),
@@ -134,13 +130,6 @@ impl ToString for ASTNode {
                 }
                 s + " END"
             }
-            ASTNode::TableFactor { relation, alias } => {
-                if let Some(alias) = alias {
-                    format!("{} AS {}", relation.to_string(), alias)
-                } else {
-                    relation.to_string()
-                }
-            }
             ASTNode::SQLSubquery(s) => format!("({})", s.to_string()),
         }
     }

src/sqlast/query.rs

@@ -5,7 +5,7 @@ pub struct SQLSelect {
     /// projection expressions
     pub projection: Vec<ASTNode>,
     /// FROM
-    pub relation: Option<Box<ASTNode>>, // TableFactor
+    pub relation: Option<TableFactor>,
     // JOIN
     pub joins: Vec<Join>,
     /// WHERE
@@ -31,7 +31,7 @@ impl ToString for SQLSelect {
                 .join(", ")
         );
         if let Some(ref relation) = self.relation {
-            s += &format!(" FROM {}", relation.as_ref().to_string());
+            s += &format!(" FROM {}", relation.to_string());
         }
         for join in &self.joins {
             s += &join.to_string();
@@ -69,9 +69,38 @@ impl ToString for SQLSelect {
     }
 }
 
+/// A table name or a parenthesized subquery with an optional alias
+#[derive(Debug, Clone, PartialEq)]
+pub enum TableFactor {
+    Table {
+        name: SQLObjectName,
+        alias: Option<SQLIdent>,
+    },
+    Derived {
+        subquery: Box<SQLSelect>,
+        alias: Option<SQLIdent>,
+    },
+}
+
+impl ToString for TableFactor {
+    fn to_string(&self) -> String {
+        let (base, alias) = match self {
+            TableFactor::Table { name, alias } => (name.to_string(), alias),
+            TableFactor::Derived { subquery, alias } => {
+                (format!("({})", subquery.to_string()), alias)
+            }
+        };
+        if let Some(alias) = alias {
+            format!("{} AS {}", base, alias)
+        } else {
+            base
+        }
+    }
+}
+
 #[derive(Debug, Clone, PartialEq)]
 pub struct Join {
-    pub relation: ASTNode, // TableFactor
+    pub relation: TableFactor,
     pub join_operator: JoinOperator,
 }
 

src/sqlparser.rs

@@ -1119,8 +1119,8 @@ impl Parser {
     pub fn parse_select(&mut self) -> Result<SQLSelect, ParserError> {
         let projection = self.parse_expr_list()?;
 
-        let (relation, joins): (Option<Box<ASTNode>>, Vec<Join>) = if self.parse_keyword("FROM") {
-            let relation = Some(Box::new(self.parse_table_factor()?));
+        let (relation, joins) = if self.parse_keyword("FROM") {
+            let relation = Some(self.parse_table_factor()?);
             let joins = self.parse_joins()?;
             (relation, joins)
         } else {
@@ -1171,20 +1171,21 @@ impl Parser {
     }
 
     /// A table name or a parenthesized subquery, followed by optional `[AS] alias`
-    pub fn parse_table_factor(&mut self) -> Result<ASTNode, ParserError> {
-        let relation = if self.consume_token(&Token::LParen) {
+    pub fn parse_table_factor(&mut self) -> Result<TableFactor, ParserError> {
+        if self.consume_token(&Token::LParen) {
             self.expect_keyword("SELECT")?;
             let subquery = self.parse_select()?;
             self.expect_token(&Token::RParen)?;
-            ASTNode::SQLSubquery(subquery)
+            Ok(TableFactor::Derived {
+                subquery: Box::new(subquery),
+                alias: self.parse_optional_alias(keywords::RESERVED_FOR_TABLE_ALIAS)?,
+            })
         } else {
-            ASTNode::SQLCompoundIdentifier(self.parse_object_name()?.0)
-        };
-        let alias = self.parse_optional_alias(keywords::RESERVED_FOR_TABLE_ALIAS)?;
-        Ok(ASTNode::TableFactor {
-            relation: Box::new(relation),
-            alias,
-        })
+            Ok(TableFactor::Table {
+                name: self.parse_object_name()?,
+                alias: self.parse_optional_alias(keywords::RESERVED_FOR_TABLE_ALIAS)?,
+            })
+        }
     }
 
     fn parse_join_constraint(&mut self, natural: bool) -> Result<JoinConstraint, ParserError> {

tests/sqlparser_generic.rs

@@ -432,6 +432,14 @@ fn parse_delimited_identifiers() {
     // check that quoted identifiers in any position remain quoted after serialization
     let sql = r#"SELECT "alias"."bar baz", "myfun"(), "simple id" FROM "a table" AS "alias""#;
     let select = verified_only_select(sql);
+    // check FROM
+    match select.relation.unwrap() {
+        TableFactor::Table { name, alias } => {
+            assert_eq!(vec![r#""a table""#.to_string()], name.0);
+            assert_eq!(r#""alias""#, alias.unwrap());
+        }
+        _ => panic!("Expecting TableFactor::Table"),
+    }
     // check SELECT
     assert_eq!(3, select.projection.len());
     assert_eq!(
@@ -515,45 +523,33 @@ fn parse_case_expression() {
 #[test]
 fn parse_implicit_join() {
     let sql = "SELECT * FROM t1, t2";
-
-    match verified_stmt(sql) {
-        SQLStatement::SQLSelect(SQLSelect { joins, .. }) => {
-            assert_eq!(joins.len(), 1);
-            assert_eq!(
-                joins[0],
-                Join {
-                    relation: ASTNode::TableFactor {
-                        relation: Box::new(ASTNode::SQLCompoundIdentifier(vec!["t2".to_string()])),
-                        alias: None,
-                    },
-                    join_operator: JoinOperator::Implicit
-                }
-            )
-        }
-        _ => assert!(false),
-    }
+    let select = verified_only_select(sql);
+    assert_eq!(
+        &Join {
+            relation: TableFactor::Table {
+                name: SQLObjectName(vec!["t2".to_string()]),
+                alias: None,
+            },
+            join_operator: JoinOperator::Implicit
+        },
+        only(&select.joins),
+    );
 }
 
 #[test]
 fn parse_cross_join() {
     let sql = "SELECT * FROM t1 CROSS JOIN t2";
-
-    match verified_stmt(sql) {
-        SQLStatement::SQLSelect(SQLSelect { joins, .. }) => {
-            assert_eq!(joins.len(), 1);
-            assert_eq!(
-                joins[0],
-                Join {
-                    relation: ASTNode::TableFactor {
-                        relation: Box::new(ASTNode::SQLCompoundIdentifier(vec!["t2".to_string()])),
-                        alias: None,
-                    },
-                    join_operator: JoinOperator::Cross
-                }
-            )
-        }
-        _ => assert!(false),
-    }
+    let select = verified_only_select(sql);
+    assert_eq!(
+        &Join {
+            relation: TableFactor::Table {
+                name: SQLObjectName(vec!["t2".to_string()]),
+                alias: None,
+            },
+            join_operator: JoinOperator::Cross
+        },
+        only(&select.joins),
+    );
 }
 
 #[test]
@@ -564,8 +560,8 @@ fn parse_joins_on() {
         f: impl Fn(JoinConstraint) -> JoinOperator,
     ) -> Join {
         Join {
-            relation: ASTNode::TableFactor {
-                relation: Box::new(ASTNode::SQLCompoundIdentifier(vec![relation.into()])),
+            relation: TableFactor::Table {
+                name: SQLObjectName(vec![relation.into()]),
                 alias,
             },
             join_operator: f(JoinConstraint::On(ASTNode::SQLBinaryExpr {
@@ -615,8 +611,8 @@ fn parse_joins_using() {
         f: impl Fn(JoinConstraint) -> JoinOperator,
     ) -> Join {
         Join {
-            relation: ASTNode::TableFactor {
-                relation: Box::new(ASTNode::SQLCompoundIdentifier(vec![relation.into()])),
+            relation: TableFactor::Table {
+                name: SQLObjectName(vec![relation.into()]),
                 alias,
             },
             join_operator: f(JoinConstraint::Using(vec!["c1".into()])),