Basis-aggregatiefuncties

Tijdreeksanalyse in SQL Server

Maham Faisal Khan

Senior Data Science Content Developer

Belangrijkste aggregatiefuncties

Aantallen

COUNT()

COUNT_BIG()

COUNT(DISTINCT)

Overige aggregaten

SUM()

MIN()

MAX()

Wat telt met COUNT()

Aantal rijen

COUNT(*)

COUNT(1)

COUNT(1/0)

Niet-NULL-waarden

COUNT(d.YR)

COUNT(NULLIF(d.YR, 1990))

Unieke tellingen

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

Years	Y2
50	49

Aggregaten filteren met CASE

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

Laten we oefenen!

Tijdreeksanalyse in SQL Server