code: function selectColumnSql (model, column, spec, alias, as) {
      // if alias is not registered then this should be a table name
      if (!this.aliases[alias]) {
          // create alias from table anme
          alias = this.getAlias(alias)
      }
      // base sql is alias.`column`
      var sql = alias+'.'+this.quoteName(column)
      // if column type is id then select HEX(alias.`column`) AS `column`
      if (spec.type === 'id' && model.binaryIds) {
          sql = 'LOWER(HEX('+sql+')) as '+this.quoteName(typeof as === 'string' ? as : column)
      }
      // if column type is data and compression then select
      // BASE_64(alias.`column`) AS `column`
      else if (spec.type === 'data' && model.compression) {
          sql = 'TO_BASE64('+sql+') as '+this.quoteName(typeof as === 'string' ? as : column)
      }
      // return column sql
      return sql
  }
docs: @function selectColumnSql
  
  bulid sql for colummn in SELECT statement
  
  @param {object} model
  @param {string} column
  @param {object} spec
  @param {string} alias
  @param {string} as
  
  @returns {string}
  
  @throws {Error}