如何减少查询执行时间

Question

 SELECT dt AS Date
,monthname
,dayname
,(
    SELECT COUNT(1)
    FROM Calendar
    WHERE DATEPART(MM, dt) = DATEPART(MM, c.dt)
        AND DATEPART(YEAR, dt) = DATEPART(YEAR, c.dt)
    ) AS daysInMonth
FROM Calendar AS c
WHERE dt BETWEEN '2000-01-01 00:00:00'
    AND '2020-02-01 00:00:00'

上述查询用于获取特定日期的特定月份的天数。这里我给出日期范围和范围之间的所有日期，我只是显示该月的日期。

该图显示了查询的结果，大约 7500 行需要 25 秒。谁能帮我减少时间。

Answer 1

试试这个。在这里，您只计算一次总数，而不是 7500 次。 同时为 dt 字段创建索引

with monthCount as (
      SELECT DATEPART(YEAR, dt) as m_year,
             DATEPART(MM, dt) as m_month
             COUNT(1) as total
      FROM Calendar
      GROUP BY 
            DATEPART(YEAR, dt),
            DATEPART(MM, dt)
)
SELECT dt AS Date
       ,monthname
       ,dayname
       ,total
FROM Calendar C
JOIN monthCount M
    on DATEPART(YEAR, C.dt) = M.m_year
   and DATEPART(MM, C.dt) = M.m_month
WHERE C.dt BETWEEN '2000-01-01 00:00:00'
               AND '2020-02-01 00:00:00'