group by和order by在springboot中連用03

1 mysql最初代碼

SELECT DATE_FORMAT(update_time, "%Y") AS year FROM t_daily
GROUP BY year
ORDER BY MIN(update_time) DESC;

參考鏈接

• 1 order by查詢的必須是原本的數據，不能是處理後的數據（year）
• 2 DATE_FORMAT(update_time, “%Y”) ：將日期字段update_time格式化爲僅剩下年份
• 3 group by和order by連用時，order by必須放在聚合函數中，聚合函數任意，不放的話報錯：

Expression #1 of ORDER BY clause is not in GROUP BY clause and contains nonaggregated column 'daily.t_daily.update_time' which is not functionally dependent on columns in GROUP BY clause; this is incompatible with sql_mode=only_full_group_by

2 springboot中

@Query("select function('date_format',d.updateTime,'%Y') as year from t_daily d group by year order by MIN(d.updateTime) desc ") //按照年份
List<String> findGroupYear(); //返回年份

• 數據渲染時發現hashmap輸出的數據是無序的，若想讓數據有序渲染到頁面，應該使用LinkedHashMap

Map<String,List<Daily>> map = new LinkedHashMap<>();