Antal och summor

SQL Server för medelnivå

Ginger Grant

Instructor

Undersöka totaler med COUNT

SELECT COUNT(*) FROM Incidents

+-----------------+
|(No column name) |
+-----------------+
|6452             | 
+-----------------+

COUNT med DISTINCT

COUNT(DISTINCT COLUMN_NAME)

COUNT med DISTINCT i T-SQL (I)

SELECT COUNT(DISTINCT Country) AS Countries
FROM Incidents

+----------------+
|Countries       |
+-----------------+
|3               |
+-----------------+

COUNT med DISTINCT i T-SQL (II)

SELECT COUNT(DISTINCT Country) AS Countries,
COUNT(DISTINCT City) AS Cities 
FROM Incidents

+----------------+-------------+
|Countries       | Cities      |
+-----------------+-------------+
|3               | 3566        |
+-----------------+-------------+

COUNT-AGGREGERING

GROUP BY kan användas med COUNT() på samma sätt som andra aggregeringsfunktioner, till exempel AVG(), MIN() och MAX()
Använd ORDER BY för att sortera värdena
- ASC returnerar de minsta värdena först (standard)
- DESC returnerar de största värdena först

COUNT med GROUP BY i T-SQL

-- Count the rows, subtotaled by Country
SELECT COUNT(*) AS TotalRowsbyCountry, Country
FROM Incidents
GROUP BY Country

+----------------------+-----------------+
|TotalRowsbyCountry   | Country         |
+----------------------+-----------------+
|5452                 |us               |
|750                  |NULL             |
|249                  |ca               |
|1                    |gb               |
+----------------------+-----------------+

COUNT med GROUP BY och ORDER BY i T-SQL (I)

-- Count the rows, subtotaled by Country
SELECT COUNT(*) AS TotalRowsbyCountry, Country
FROM Incidents
GROUP BY Country 
ORDER BY Country ASC

+----------------------+-----------------+
|TotalRowsbyCountry   | Country         |
+----------------------+-----------------+
|750                  |NULL             |
|249                  |ca               |
|1                    |gb               |
|5452                 |us               |
+----------------------+-----------------+

COUNT med GROUP BY och ORDER BY i T-SQL (II)

-- Count the rows, subtotaled by Country
SELECT COUNT(*) AS TotalRowsbyCountry, Country
FROM Incidents
GROUP BY Country 
ORDER BY Country DESC

+----------------------+-----------------+
|TotalRowsbyCountry   | Country         |
+----------------------+-----------------+
|5452                 |us               |
|1                    |gb               |
|249                  |ca               |
|750                  |NULL             |
+----------------------+-----------------+

Kolumnsummor med SUM

SUM() beräknar den numeriska summan av värdena i en kolumn
Funktionen följer samma mönster som övriga aggregeringar
Kombinera med GROUP BY för delsummor baserade på angivna kolumner

Summera kolumnvärden i T-SQL

-- Calculate the values subtotaled by Country
SELECT SUM(DurationSeconds) AS TotalDuration, Country
FROM Incidents
GROUP BY Country

+----------+--------------------+
|Country   |TotalDuration       |
+----------+--------------------+
|us        |17024946.750001565  |
|null      |18859192.800000012  |
|ca        |200975              |
|gb        |120                 |
+----------+--------------------+

Nu kör vi en övning!

SQL Server för medelnivå