@Override
  public ValidationErrors validate(final Database database) {
    final ValidationErrors validationErrors;

    if ((database instanceof DerbyDatabase || database instanceof H2Database)
        && getTableName() == null) {
      validationErrors = new ValidationErrors();
      validationErrors.addError("tableName is required for " + database.getDatabaseProductName());
    } else {
      final IndexExistsPrecondition precondition = new IndexExistsPrecondition();
      precondition.setCatalogName(getCatalogName());
      precondition.setSchemaName(getSchemaName());
      precondition.setTableName(getTableName());
      precondition.setIndexName(getIndexName());
      precondition.setColumnNames(getColumnNames());
      validationErrors = precondition.validate(database);
    }
    return validationErrors;
  }
  protected Column readColumn(CachedRow columnMetadataResultSet, Relation table, Database database)
      throws SQLException, DatabaseException {
    String rawTableName = (String) columnMetadataResultSet.get("TABLE_NAME");
    String rawColumnName = (String) columnMetadataResultSet.get("COLUMN_NAME");
    String rawSchemaName =
        StringUtils.trimToNull((String) columnMetadataResultSet.get("TABLE_SCHEM"));
    String rawCatalogName =
        StringUtils.trimToNull((String) columnMetadataResultSet.get("TABLE_CAT"));
    String remarks = StringUtils.trimToNull((String) columnMetadataResultSet.get("REMARKS"));
    if (remarks != null) {
      remarks = remarks.replace("''", "'"); // come back escaped sometimes
    }

    Column column = new Column();
    column.setName(StringUtils.trimToNull(rawColumnName));
    column.setRelation(table);
    column.setRemarks(remarks);

    if (database instanceof OracleDatabase) {
      String nullable = columnMetadataResultSet.getString("NULLABLE");
      if (nullable.equals("Y")) {
        column.setNullable(true);
      } else {
        column.setNullable(false);
      }
    } else {
      int nullable = columnMetadataResultSet.getInt("NULLABLE");
      if (nullable == DatabaseMetaData.columnNoNulls) {
        column.setNullable(false);
      } else if (nullable == DatabaseMetaData.columnNullable) {
        column.setNullable(true);
      } else if (nullable == DatabaseMetaData.columnNullableUnknown) {
        LogFactory.getLogger()
            .info("Unknown nullable state for column " + column.toString() + ". Assuming nullable");
        column.setNullable(true);
      }
    }

    if (database.supportsAutoIncrement()) {
      if (table instanceof Table) {
        if (columnMetadataResultSet.containsColumn("IS_AUTOINCREMENT")) {
          String isAutoincrement = (String) columnMetadataResultSet.get("IS_AUTOINCREMENT");
          isAutoincrement = StringUtils.trimToNull(isAutoincrement);
          if (isAutoincrement == null) {
            column.setAutoIncrementInformation(null);
          } else if (isAutoincrement.equals("YES")) {
            column.setAutoIncrementInformation(new Column.AutoIncrementInformation());
          } else if (isAutoincrement.equals("NO")) {
            column.setAutoIncrementInformation(null);
          } else if (isAutoincrement.equals("")) {
            LogFactory.getLogger()
                .info(
                    "Unknown auto increment state for column "
                        + column.toString()
                        + ". Assuming not auto increment");
            column.setAutoIncrementInformation(null);
          } else {
            throw new UnexpectedLiquibaseException(
                "Unknown is_autoincrement value: '" + isAutoincrement + "'");
          }
        } else {
          // probably older version of java, need to select from the column to find out if it is
          // auto-increment
          String selectStatement;
          if (database.getDatabaseProductName().startsWith("DB2 UDB for AS/400")) {
            selectStatement =
                "select "
                    + database.escapeColumnName(
                        rawCatalogName, rawSchemaName, rawTableName, rawColumnName)
                    + " from "
                    + rawSchemaName
                    + "."
                    + rawTableName
                    + " where 0=1";
            LogFactory.getLogger().debug("rawCatalogName : <" + rawCatalogName + ">");
            LogFactory.getLogger().debug("rawSchemaName : <" + rawSchemaName + ">");
            LogFactory.getLogger().debug("rawTableName : <" + rawTableName + ">");
            LogFactory.getLogger().debug("raw selectStatement : <" + selectStatement + ">");

          } else {
            selectStatement =
                "select "
                    + database.escapeColumnName(
                        rawCatalogName, rawSchemaName, rawTableName, rawColumnName)
                    + " from "
                    + database.escapeTableName(rawCatalogName, rawSchemaName, rawTableName)
                    + " where 0=1";
          }
          LogFactory.getLogger()
              .debug(
                  "Checking "
                      + rawTableName
                      + "."
                      + rawCatalogName
                      + " for auto-increment with SQL: '"
                      + selectStatement
                      + "'");
          Connection underlyingConnection =
              ((JdbcConnection) database.getConnection()).getUnderlyingConnection();
          Statement statement = null;
          ResultSet columnSelectRS = null;

          try {
            statement = underlyingConnection.createStatement();
            columnSelectRS = statement.executeQuery(selectStatement);
            if (columnSelectRS.getMetaData().isAutoIncrement(1)) {
              column.setAutoIncrementInformation(new Column.AutoIncrementInformation());
            } else {
              column.setAutoIncrementInformation(null);
            }
          } finally {
            try {
              if (statement != null) {
                statement.close();
              }
            } catch (SQLException ignore) {
            }
            if (columnSelectRS != null) {
              columnSelectRS.close();
            }
          }
        }
      }
    }

    DataType type = readDataType(columnMetadataResultSet, column, database);
    column.setType(type);

    column.setDefaultValue(readDefaultValue(columnMetadataResultSet, column, database));

    return column;
  }