@Override
  public String getDropUniqueConstraintStatement(String tableName, String constraintName){

    UniqueKeyConstraint uniqueKeyConstraint = new UniqueKeyConstraint();
    uniqueKeyConstraint.setName(constraintName);

    Writer writer = new StringWriter();
    TableDefinition tableDefinition = new TableDefinition();
    tableDefinition.setName(tableName);
    tableDefinition.buildUniqueConstraintDeletionWriter(createStubAbstractSessionFromPlatform(databasePlatform),
                                                         uniqueKeyConstraint, writer);

    return writer.toString();
  }
Write create table statement to writer
TODO default Value of column not supported
ambari-server/src/main/java/org/apache/ambari/server/orm/helpers/dbms/GenericDbmsHelper.java