Fix: JOIN should require ON condition

src/parser/mod.rs

@@ -10155,10 +10155,30 @@ impl<'a> Parser<'a> {
                 };
                 let relation = self.parse_table_factor()?;
                 let join_constraint = self.parse_join_constraint(natural)?;
+                let join_operator = join_operator_type(join_constraint);
+
+                let requires_constraint = match join_operator {
+                    JoinOperator::Inner(JoinConstraint::None)
+                    | JoinOperator::LeftOuter(JoinConstraint::None)
+                    | JoinOperator::RightOuter(JoinConstraint::None)
+                    | JoinOperator::FullOuter(JoinConstraint::None)
+                    | JoinOperator::LeftSemi(JoinConstraint::None)
+                    | JoinOperator::RightSemi(JoinConstraint::None)
+                    | JoinOperator::LeftAnti(JoinConstraint::None)
+                    | JoinOperator::RightAnti(JoinConstraint::None)
+                    | JoinOperator::Semi(JoinConstraint::None)
+                    | JoinOperator::Anti(JoinConstraint::None) => !natural,
+                    _ => false,
+                };
+
+                if requires_constraint {
+                    self.expected("ON, or USING after JOIN", self.peek_token())?
+                }
+
                 Join {
                     relation,
                     global,
-                    join_operator: join_operator_type(join_constraint),
+                    join_operator,
                 }
             };
             joins.push(join);
@@ -10967,7 +10987,6 @@ impl<'a> Parser<'a> {
             Ok(JoinConstraint::Using(columns))
         } else {
             Ok(JoinConstraint::None)
-            //self.expected("ON, or USING after JOIN", self.peek_token())
         }
     }
 

tests/sqlparser_common.rs

@@ -7613,7 +7613,7 @@ fn lateral_derived() {
 
 #[test]
 fn lateral_function() {
-    let sql = "SELECT * FROM customer LEFT JOIN LATERAL generate_series(1, customer.id)";
+    let sql = "SELECT * FROM customer CROSS JOIN LATERAL generate_series(1, customer.id)";
     let actual_select_only = verified_only_select(sql);
     let expected = Select {
         distinct: None,
@@ -7654,7 +7654,7 @@ fn lateral_function() {
                     alias: None,
                 },
                 global: false,
-                join_operator: JoinOperator::LeftOuter(JoinConstraint::None),
+                join_operator: JoinOperator::CrossJoin,
             }],
         }],
         lateral_views: vec![],
@@ -12368,6 +12368,50 @@ fn parse_create_table_select() {
     }
 }
 
+#[test]
+fn parse_no_condition_join_strategy() {
+    let dialects = all_dialects_where(|d| d.supports_create_table_select());
+
+    let join_types = vec![
+        "JOIN",
+        "INNER JOIN",
+        "LEFT JOIN",
+        "LEFT OUTER JOIN",
+        "RIGHT JOIN",
+        "RIGHT OUTER JOIN",
+        "FULL JOIN",
+        "FULL OUTER JOIN",
+        "CROSS JOIN",
+        "NATURAL JOIN",
+        "LEFT SEMI JOIN",
+        "RIGHT SEMI JOIN",
+        "LEFT ANTI JOIN",
+        "RIGHT ANTI JOIN",
+        "SEMI JOIN",
+        "ANTI JOIN",
+    ];
+
+    for join in join_types {
+        let sql = format!(
+            "SELECT * FROM (SELECT 1 AS id, 'Foo' AS name) AS l {} (SELECT 1 AS id, 'Bar' AS name) AS r",
+            join
+        );
+        let result = dialects.parse_sql_statements(&sql);
+        if join.starts_with("CROSS") || join.starts_with("NATURAL") {
+            // CROSS JOIN and NATURAL JOIN don't require ON or USING clauses
+            assert!(result.is_ok());
+        } else {
+            // Other joins require ON or USING clauses
+            assert_eq!(
+                result.unwrap_err(),
+                ParserError::ParserError(
+                    "Expected: ON, or USING after JOIN, found: EOF".to_string()
+                )
+            );
+        }
+    }
+}
+
 #[test]
 fn test_reserved_keywords_for_identifiers() {
     let dialects = all_dialects_where(|d| d.is_reserved_for_identifier(Keyword::INTERVAL));

tests/sqlparser_hive.rs

@@ -285,7 +285,7 @@ fn test_distribute_by() {
 
 #[test]
 fn no_join_condition() {
-    let join = "SELECT a, b FROM db.table_name JOIN a";
+    let join = "SELECT a, b FROM db.table_name CROSS JOIN a";
     hive().verified_stmt(join);
 }