Support Alter Table Add Unique Constraint (#708)

Author: rfscholte

src/main/java/net/sf/jsqlparser/statement/alter/AlterExpression.java

@@ -232,8 +232,11 @@ public String toString() {
         } else if (pkColumns != null) {
             b.append("PRIMARY KEY (").append(PlainSelect.getStringList(pkColumns)).append(')');
         } else if (ukColumns != null) {
-            b.append("UNIQUE KEY ").append(ukName).append(" (").append(PlainSelect.
-                    getStringList(ukColumns)).append(")");
+            b.append("UNIQUE");
+            if (ukName != null) {
+              b.append(" KEY ").append(ukName);    
+            }
+            b.append(" (").append(PlainSelect.getStringList(ukColumns)).append(")");
         } else if (fkColumns != null) {
             b.append("FOREIGN KEY (").append(PlainSelect.getStringList(fkColumns)).
                     append(") REFERENCES ").append(fkSourceTable).append(" (").append(

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

@@ -3782,7 +3782,7 @@ AlterExpression AlterExpression():
                 ("," alterExpressionColumnDataType = AlterExpressionColumnDataType() { alterExp.addColDataType(alterExpressionColumnDataType); } )* ")"
         )
         |
-        ( <K_UNIQUE> <K_KEY> (tk=<S_IDENTIFIER>    | tk=<S_QUOTED_IDENTIFIER>) columnNames=ColumnsNamesList() { alterExp.setUkName(tk.image); alterExp.setUkColumns(columnNames); } )
+        ( <K_UNIQUE> (<K_KEY> (tk=<S_IDENTIFIER> | tk=<S_QUOTED_IDENTIFIER>) { alterExp.setUkName(tk.image); } )? columnNames=ColumnsNamesList() { alterExp.setUkColumns(columnNames); } )
         |
 //following two choices regarding foreign keys should be merged
         ( <K_FOREIGN> <K_KEY> columnNames=ColumnsNamesList() { alterExp.setFkColumns(columnNames); }

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

@@ -102,6 +102,11 @@ public void testAlterTableAddConstraintWithConstraintState() throws JSQLParserEx
     public void testAlterTableAddConstraintWithConstraintState2() throws JSQLParserException {
         assertSqlCanBeParsedAndDeparsed("ALTER TABLE RESOURCELINKTYPE ADD CONSTRAINT RESOURCELINKTYPE_PRIMARYKEY PRIMARY KEY (PRIMARYKEY) DEFERRABLE NOVALIDATE");
     }
+    
+    @Test
+    public void testAlterTableAddUniqueConstraint() throws JSQLParserException {
+        assertSqlCanBeParsedAndDeparsed("ALTER TABLE Persons ADD UNIQUE (ID)");
+    }
 
     @Test
     public void testAlterTableForgeignKey2() throws JSQLParserException {