基本聚合函数

SQL Server 中的时间序列分析

Maham Faisal Khan

Senior Data Science Content Developer

关键聚合函数

计数

COUNT()

COUNT_BIG()

COUNT(DISTINCT)

其他聚合

SUM()

MIN()

MAX()

COUNT() 会计入什么

行数

COUNT(*)

COUNT(1)

COUNT(1/0)

非 NULL 值

COUNT(d.YR)

COUNT(NULLIF(d.YR, 1990))

去重计数

SELECT
    COUNT(DISTINCT c.CalendarYear) AS Years,
    COUNT(DISTINCT NULLIF(c.CalendarYear, 2010)) AS Y2
FROM dbo.Calendar c;

Years	Y2
50	49

用 CASE 过滤聚合

SELECT
    MAX(CASE WHEN ir.IncidentTypeID = 1
            THEN ir.IncidentDate
            ELSE NULL
        END) AS I1,
    MAX(CASE WHEN ir.IncidentTypeID = 2
            THEN ir.IncidentDate
            ELSE NULL
        END) AS I2,
FROM dbo.IncidentRollup ir;

I1	I2
2020-06-30	2020-06-29

Passons à la pratique !

SQL Server 中的时间序列分析