fixes #320 (#576)

* fixes #320

Author: tmnsur

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

@@ -3477,7 +3477,33 @@ AlterExpression AlterExpression():
                 checkCs.setExpression(exp);
                 alterExp.setIndex(checkCs);
             }
-           ) )
+            )
+            |
+            (
+                tk=<K_UNIQUE> tk2=<K_KEY>
+                  columnNames=ColumnsNamesList()
+                  {
+                      index = new NamedConstraint();
+                      index.setName(sk3);
+                      index.setType(tk.image + " " + tk2.image);
+                      index.setColumnsNames(columnNames);
+                      alterExp.setIndex(index);
+                  }
+                  constraints=AlterExpressionConstraintState() { alterExp.setConstraints(constraints); }
+            )
+            |
+            (
+                tk=<K_KEY>
+                  columnNames=ColumnsNamesList()
+                  {
+                      index = new NamedConstraint();
+                      index.setName(sk3);
+                      index.setType(tk.image);
+                      index.setColumnsNames(columnNames);
+                      alterExp.setIndex(index);
+                  }
+                  constraints=AlterExpressionConstraintState() { alterExp.setConstraints(constraints); }
+            ) )
         )
         )
     )

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

@@ -3,6 +3,7 @@
 import static net.sf.jsqlparser.test.TestUtils.assertSqlCanBeParsedAndDeparsed;
 import static net.sf.jsqlparser.test.TestUtils.assertStatementCanBeDeparsedAs;
 
+import java.util.Arrays;
 import java.util.List;
 
 import junit.framework.TestCase;
@@ -252,4 +253,28 @@ public void testDropColumnRestrictIssue551() throws JSQLParserException {
         assertStatementCanBeDeparsedAs(stmt, "ALTER TABLE table1 DROP COLUMN NewColumn");
 
     }
+    
+    public void testAddConstraintKeyIssue320() throws JSQLParserException {
+        String tableName = "table1";
+        String columnName1 = "col1";
+        String columnName2 = "col2";
+        String columnName3 = "col3";
+        String columnName4 = "col4";
+        String constraintName1 = "table1_constraint_1";
+        String constraintName2 = "table1_constraint_2";
+
+        for(String constraintType : Arrays.asList("UNIQUE KEY", "KEY")) {
+            Statement stmt = CCJSqlParserUtil.parse("ALTER TABLE " + tableName + " ADD CONSTRAINT " + constraintName1 + " " + constraintType + " (" + columnName1 + ")");
+
+            assertStatementCanBeDeparsedAs(stmt, "ALTER TABLE " + tableName + " ADD CONSTRAINT " + constraintName1 + " " + constraintType + " (" + columnName1 + ")");
+
+            stmt = CCJSqlParserUtil.parse("ALTER TABLE " + tableName + " ADD CONSTRAINT " + constraintName1 + " " + constraintType + " (" + columnName1 + ", " + columnName2 + ")");
+
+            assertStatementCanBeDeparsedAs(stmt, "ALTER TABLE " + tableName + " ADD CONSTRAINT " + constraintName1 + " " + constraintType + " (" + columnName1 + ", " + columnName2 + ")");
+
+            stmt = CCJSqlParserUtil.parse("ALTER TABLE " + tableName + " ADD CONSTRAINT " + constraintName1 + " " + constraintType + " (" + columnName1 + ", " + columnName2 + "), ADD CONSTRAINT " + constraintName2 + " " + constraintType + " (" + columnName3 + ", " + columnName4 + ")");
+
+            assertStatementCanBeDeparsedAs(stmt, "ALTER TABLE " + tableName + " ADD CONSTRAINT " + constraintName1 + " " + constraintType + " (" + columnName1 + ", " + columnName2 + "), ADD CONSTRAINT " + constraintName2 + " " + constraintType + " (" + columnName3 + ", " + columnName4 + ")");
+        }
+    }
 }