Allow foreign table constraint without columns (#1608)

Author: ramnivas

src/ast/ddl.rs

@@ -885,12 +885,14 @@ impl fmt::Display for TableConstraint {
             } => {
                 write!(
                     f,
-                    "{}FOREIGN KEY ({}) REFERENCES {}({})",
+                    "{}FOREIGN KEY ({}) REFERENCES {}",
                     display_constraint_name(name),
                     display_comma_separated(columns),
                     foreign_table,
-                    display_comma_separated(referred_columns),
                 )?;
+                if !referred_columns.is_empty() {
+                    write!(f, "({})", display_comma_separated(referred_columns))?;
+                }
                 if let Some(action) = on_delete {
                     write!(f, " ON DELETE {action}")?;
                 }

src/parser/mod.rs

@@ -6830,7 +6830,7 @@ impl<'a> Parser<'a> {
                 let columns = self.parse_parenthesized_column_list(Mandatory, false)?;
                 self.expect_keyword(Keyword::REFERENCES)?;
                 let foreign_table = self.parse_object_name(false)?;
-                let referred_columns = self.parse_parenthesized_column_list(Mandatory, false)?;
+                let referred_columns = self.parse_parenthesized_column_list(Optional, false)?;
                 let mut on_delete = None;
                 let mut on_update = None;
                 loop {

tests/sqlparser_common.rs

@@ -4167,6 +4167,7 @@ fn parse_alter_table_constraints() {
     check_one("UNIQUE (id)");
     check_one("FOREIGN KEY (foo, bar) REFERENCES AnotherTable(foo, bar)");
     check_one("CHECK (end_date > start_date OR end_date IS NULL)");
+    check_one("CONSTRAINT fk FOREIGN KEY (lng) REFERENCES othertable4");
 
     fn check_one(constraint_text: &str) {
         match alter_table_op(verified_stmt(&format!(