Improve DELETE FROM parsing (4.4/4.4)

Store (and parse) `table_name: SQLObjectName` instead of
`relation: Option<Box<ASTNode>>`, which can be an arbitrary expression.

Also remove the `Option<>`: the table name is not optional in any dialects
I'm familiar with. While the FROM keyword itself _is_ optional in some
dialects, there are more things to implement for those dialects, see
https://stackoverflow.com/a/4484271/1026

Author: nickolay

src/sqlast/mod.rs

@@ -179,7 +179,7 @@ pub enum SQLStatement {
     /// DELETE
     SQLDelete {
         /// FROM
-        relation: Option<Box<ASTNode>>,
+        table_name: SQLObjectName,
         /// WHERE
         selection: Option<Box<ASTNode>>,
     },
@@ -279,13 +279,10 @@ impl ToString for SQLStatement {
                 s
             }
             SQLStatement::SQLDelete {
-                relation,
+                table_name,
                 selection,
             } => {
-                let mut s = String::from("DELETE");
-                if let Some(relation) = relation {
-                    s += &format!(" FROM {}", relation.as_ref().to_string());
-                }
+                let mut s = format!("DELETE FROM {}", table_name.to_string());
                 if let Some(selection) = selection {
                     s += &format!(" WHERE {}", selection.as_ref().to_string());
                 }

src/sqlparser.rs

@@ -1105,20 +1105,16 @@ impl Parser {
     }
 
     pub fn parse_delete(&mut self) -> Result<SQLStatement, ParserError> {
-        let relation: Option<Box<ASTNode>> = if self.parse_keyword("FROM") {
-            Some(Box::new(self.parse_subexpr(0)?)) /* TBD (4) */
-        } else {
-            None
-        };
-
+        self.expect_keyword("FROM")?;
+        let table_name = self.parse_object_name()?;
         let selection = if self.parse_keyword("WHERE") {
             Some(Box::new(self.parse_expr()?))
         } else {
             None
         };
 
         Ok(SQLStatement::SQLDelete {
-            relation,
+            table_name,
             selection,
         })
     }

tests/sqlparser_generic.rs

@@ -8,16 +8,10 @@ use sqlparser::sqltokenizer::*;
 
 #[test]
 fn parse_delete_statement() {
-    let sql: &str = "DELETE FROM 'table'";
-
-    match verified_stmt(&sql) {
-        SQLStatement::SQLDelete { relation, .. } => {
-            assert_eq!(
-                Some(Box::new(ASTNode::SQLValue(Value::SingleQuotedString(
-                    "table".to_string()
-                )))),
-                relation
-            );
+    let sql = "DELETE FROM \"table\"";
+    match verified_stmt(sql) {
+        SQLStatement::SQLDelete { table_name, .. } => {
+            assert_eq!(SQLObjectName(vec!["\"table\"".to_string()]), table_name);
         }
 
         _ => assert!(false),
@@ -26,23 +20,17 @@ fn parse_delete_statement() {
 
 #[test]
 fn parse_where_delete_statement() {
-    let sql: &str = "DELETE FROM 'table' WHERE name = 5";
-
     use self::ASTNode::*;
     use self::SQLOperator::*;
 
-    match verified_stmt(&sql) {
+    let sql = "DELETE FROM foo WHERE name = 5";
+    match verified_stmt(sql) {
         SQLStatement::SQLDelete {
-            relation,
+            table_name,
             selection,
             ..
         } => {
-            assert_eq!(
-                Some(Box::new(ASTNode::SQLValue(Value::SingleQuotedString(
-                    "table".to_string()
-                )))),
-                relation
-            );
+            assert_eq!(SQLObjectName(vec!["foo".to_string()]), table_name);
 
             assert_eq!(
                 SQLBinaryExpr {