hive 查询当年天数

### 在 Hive 中查询当前年的总天数

为了计算当前年的总天数，在Hive中可以采用如下方法：

通过判断当前年份是否为闰年来决定该年有365天还是366天。这可以通过编写一个自定义的SQL语句来实现，利用`year()`函数获取当前年份，并进一步确定这一年内二月份的具体天数。

WITH leap_year_check AS (
  SELECT 
    year(current_date) as yr,
    CASE 
      WHEN (year(current_date) % 4 = 0 AND year(current_date) % 100 != 0) OR year(current_date) % 400 = 0 THEN 'Leap Year'
      ELSE 'Not Leap Year' 
    END as is_leap_year
),
feb_days AS (
  SELECT 
    yr, 
    is_leap_year,
    CASE 
      WHEN is_leap_year = 'Leap Year' THEN 29 
      ELSE 28 
    END as feb_day_count
)
SELECT 
  yr,
  SUM(CASE 
        WHEN month = 2 THEN feb_day_count
        ELSE day_in_month 
      END) OVER () as total_days_of_year
FROM 
  feb_days LATERAL VIEW posexplode(array(
    struct(1,'January',31),struct(2,'February',feb_day_count),
    struct(3,'March',31),struct(4,'April',30),
    struct(5,'May',31),struct(6,'June',30),
    struct(7,'July',31),struct(8,'August',31),
    struct(9,'September',30),struct(10,'October',31),
    struct(11,'November',30),struct(12,'December',31))) exploded_table AS (month,day_in_month)
LIMIT 1;

上述脚本首先创建了一个临时表用于检测给定年份是不是闰年[^2]；接着基于这个信息构建另一个表格以获得当年二月的确切天数；最后一步则是汇总每个月应有的天数并给出整年的总计天数值。