fixes #551

Author: wumpz

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

@@ -3462,7 +3462,7 @@ AlterExpression AlterExpression():
             alterExp.setOperation(AlterOperation.DROP);
         }
          (
-             (  <K_COLUMN>
+             (  (LOOKAHEAD(2) <K_COLUMN>)?
                 (tk=<S_IDENTIFIER>    | tk=<S_QUOTED_IDENTIFIER>)
                      {
                             alterExp.setColumnName(tk.image);

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

@@ -244,4 +244,12 @@ public void testAlterTableAddColumnKeywordTypes() throws JSQLParserException {
     public void testDropColumnRestrictIssue510() throws JSQLParserException {
         assertSqlCanBeParsedAndDeparsed("ALTER TABLE TABLE1 DROP COLUMN NewColumn CASCADE");
     }
+    
+    public void testDropColumnRestrictIssue551() throws JSQLParserException {
+        Statement stmt = CCJSqlParserUtil.parse("ALTER TABLE table1 DROP NewColumn");
+        
+        // COLUMN keyword appears in deparsed statement, drop becomes all caps
+        assertStatementCanBeDeparsedAs(stmt, "ALTER TABLE table1 DROP COLUMN NewColumn");
+        
+    }
 }