mysql查询如何去掉多余零

/**
     * 指定查询字段
     * @access public
     * @param mixed $field 字段信息
     * @param mixed $format 需要去掉多余0的 decimal字段
     * @return $this
     */
    public function field($field,$format=null)
    {
        if (empty($field)) {
            return $this;
        } elseif ($field instanceof Raw) {
            $this->options['field'][] = $field;
            return $this;
        }

        if (is_string($field)) {
            if (preg_match('/[\<\'\"\(]/', $field)) {
                return $this->fieldRaw($field);
            }

            $field = array_map('trim', explode(',', $field));
        }

        if (true === $field) {
            // 获取全部字段
            $fields = $this->getTableFields();
            $field  = $fields ?: ['*'];
        }

        if (isset($this->options['field'])) {
            $field = array_merge((array) $this->options['field'], $field);
        }
        if ($format) {
            $castField = [];
            if(is_string($format)) $format = explode(',',$format);
            if(is_array($format)){
                foreach($format as $v){
                    $asField = str_replace(".","_",$v);
                    $castField[] = '0+cast('.$v.' as char) AS '.$asField;
                }
            }
            $field = array_merge($field,$castField);
        }
        $this->options['field'] = array_unique($field);
        return $this;
    }

SELECT
    id,
    chat_id,
    content,
    create_time 
FROM
    ( SELECT id, chat_id, content, create_time FROM im_chat_message ORDER BY create_time DESC ) a 
GROUP BY
    chat_id 
ORDER BY
    create_time DESC

SELECT
    id,
    chat_id,
    content,
    create_time 
FROM
    ( SELECT id, chat_id, content, create_time FROM im_chat_message ORDER BY create_time DESC LIMIT 999999999 ) a 
GROUP BY
    chat_id 
ORDER BY
    create_time DESC

ROW_NUMBER() over ( PARTITION BY chat_id ORDER BY create_time DESC )

SELECT
    id,
    chat_id,
    content,
    create_time 
FROM
    (
    SELECT
        id,
        chat_id,
        content,
        create_time,
        ROW_NUMBER() over ( PARTITION BY chat_id ORDER BY create_time DESC ) AS rn 
    FROM
        im_chat_message 
    ORDER BY
        create_time DESC 
    ) a 
WHERE
    rn =1

 WHERE
   1 =1
   <if test="null != query.minId">
      and id &lt; #{query.minId}
   </if>
 LIMIT #{query.size}