课程简介

SQL Server 中的函数与存储过程编写

Meghan Kwartler

IT Consultant

课程目标

使用 SQL 日期函数进行时间型探索性数据分析（EDA）
创建、更新、执行用户自定义函数
创建、更新、执行存储过程
先修课程
- SQL Server 入门
- SQL 中的数据连接
- 中级 SQL Server

时间型 EDA

事务型数据集
- CapitalBikeShare
- YellowTripTaxi
探索性数据分析（EDA）流程
- 迭代式
- 无固定问题清单
- 保持好奇！
- 减少返工

EDA 可视化

用于 EDA 的 SQL 函数

-- CONVERT 语法：  
CONVERT ( data_type [ ( length ) ] , expression [ , style ] )  
-- 根据 data_type 返回表达式

-- DATEPART 语法
DATEPART ( datepart , date ) 
-- 返回 int

-- DATENAME 语法
DATENAME ( datepart , date ) 
-- 返回 nvarchar

-- DATEDIFF 语法
DATEDIFF ( datepart , startdate , enddate ) 
-- 返回 int；不能使用 datepart 的 weekday 值

-- datepart 取值 = year, quarter, month, dayofyear, day, week, weekday, hour, 
-- minute, second, microsecond, nanosecond

-- CONVERT
SELECT 
  TOP 1 PickupDate, 
  CONVERT (DATE, PickupDate) AS DateOnly 
FROM YellowTripData

+-----------------------------+------------+
| PickupDate                  | DateOnly   |
|-----------------------------+------------|
| 2017-01-09 11:52:13.0000000 | 2017-01-09 |
+-----------------------------+------------+

-- DATEPART
SELECT 
  TOP 3 COUNT(ID) AS NumberofRides, 
  DATEPART(HOUR, PickupDate) AS Hour 
FROM YellowTripData 
GROUP BY DATEPART(HOUR, PickupDate) 
ORDER BY COUNT(ID) DESC

+----------------------+
| NumberOfRides | Hour |
|----------------------+
| 616281        | 18   |
| 616281        | 19   |
| 540629        | 17   |
+---------------+------+

--DATENAME
SELECT 
  TOP 3 ROUND(
    SUM(FareAmount), 
    0
  ) as TotalFareAmt, 
  DATENAME(WEEKDAY, PickupDate) AS DayofWeek 
FROM YellowTripData 
GROUP BY DATENAME (WEEKDAY, PickupDate) 
ORDER BY SUM(FareAmount) DESC;

+--------------------------+
| TotalFareAmt | DayofWeek |
|--------------------------+
| 19026645     | Sunday    |
| 18749482     | Tuesday   |
| 17213351     | Thursday  |
+--------------+-----------+

--DATEDIFF
SELECT 
  AVG(
    DATEDIFF(SECOND, PickupDate, DropOffDate)/ 60
  ) AS AvgRideLengthInMin 
FROM YellowTripData 
WHERE DATENAME(WEEKDAY, PickupDate) = 'Sunday';

+--------------------+
| AvgRideLengthInMin |
|--------------------+
| 13                 |
+--------------------+

Passons à la pratique !

SQL Server 中的函数与存储过程编写