fixes #981

Author: wumpz

src/main/jjtree/net/sf/jsqlparser/parser/JSqlParserCC.jjt

@@ -4420,6 +4420,10 @@ AlterExpression AlterExpression():
                     fkIndex.setReferencedColumnNames(columnNames);
                     alterExp.setIndex(fkIndex);
                 }
+                [<K_ON> <K_DELETE>
+                            (<K_CASCADE> { fkIndex.setOnDeleteReferenceOption("CASCADE"); }
+                            | <K_RESTRICT> { fkIndex.setOnDeleteReferenceOption("RESTRICT"); }
+                            | <K_SET> <K_NULL> { fkIndex.setOnDeleteReferenceOption("SET NULL"); } ) ]
                 constraints=AlterExpressionConstraintState() { alterExp.setConstraints(constraints); }
             )
             |

src/test/java/net/sf/jsqlparser/statement/alter/AlterTest.java

@@ -414,4 +414,19 @@ public void testAlterTableRenameColumn() throws JSQLParserException {
         assertEquals(expression.getColOldName(), "\"test_column\"");
         assertEquals(expression.getColumnName(), "\"test_c\"");
     }
+    
+    @Test
+    public void testAlterTableForeignKeyIssue981() throws JSQLParserException {
+        assertSqlCanBeParsedAndDeparsed(
+                "ALTER TABLE atconfigpro " +
+                "ADD CONSTRAINT atconfigpro_atconfignow_id_foreign FOREIGN KEY (atconfignow_id) REFERENCES atconfignow(id) ON DELETE CASCADE, " +
+                "ADD CONSTRAINT atconfigpro_attariff_id_foreign FOREIGN KEY (attariff_id) REFERENCES attariff(id) ON DELETE CASCADE");
+    }
+    
+    @Test
+    public void testAlterTableForeignKeyIssue981_2() throws JSQLParserException {
+        assertSqlCanBeParsedAndDeparsed(
+                "ALTER TABLE atconfigpro " +
+                "ADD CONSTRAINT atconfigpro_atconfignow_id_foreign FOREIGN KEY (atconfignow_id) REFERENCES atconfignow(id) ON DELETE CASCADE");
+    }
 }