code: static String getSqlAddColumn(EntityType entityType, Attribute attr, ColumnMode columnMode) {
      StringBuilder sql = new StringBuilder("ALTER TABLE ");
  
      String columnSql = getSqlColumn(entityType, attr, columnMode);
      sql.append(getTableName(entityType)).append(" ADD ").append(columnSql);
  
      List<String> sqlTableConstraints = getSqlTableConstraints(entityType, attr);
      if (!sqlTableConstraints.isEmpty()) {
        sqlTableConstraints.forEach(
            sqlTableConstraint -> sql.append(",ADD ").append(sqlTableConstraint));
      }
      return sql.toString();
    }
docs: Returns SQL string to add a column to an existing table.
  
  @param entityType entity meta data
  @param attr attribute
  @param columnMode column mode
  @return SQL string