Filtrering med HAVING

Förbättra frågeprestanda i SQL Server

Dean Smith

Founder, Atamai Analytics

HAVINGs bearbetningsordning

1.  FROM

4.  WHERE

6.  HAVING

7.  SELECT

Gruppering med WHERE-radfilter

SELECT Team, 
    SUM(TotalPoints) AS TotalSGTeamPoints
FROM PlayerStats
WHERE Position = 'SG'
GROUP BY Team

Team	TotalSGTeamPoints
ATL	2034
BOS	1606
BRK	2126
CHI	2905
CHO	2661
CLE	2489
...	...

Radfiltrering med HAVING

SELECT Team, 
    SUM(TotalPoints) AS TotalSGTeamPoints
FROM PlayerStats
WHERE Position = 'SG'
GROUP BY Team

SELECT Team, 
    SUM(TotalPoints) AS TotalSGTeamPoints
FROM PlayerStats
--WHERE Position = 'SG'
GROUP BY Team, Position
HAVING Position = 'SG'

Använd inte HAVING för att filtrera enskilda eller ogruppperade rader

Team	TotalSGTeamPoints
ATL	2034
BOS	1606
BRK	2126
CHI	2905
CHO	2661
CLE	2489
...	...

Aggregering per grupp

SELECT 
    Team, 
    SUM(DRebound+ORebound) AS TotRebounds,
    SUM(DRebound) AS TotDef,
    SUM(ORebound) AS TotOff
FROM PlayerStats
GROUP BY Team;

Team	TotRebounds	TotDef	TotOff
ATL	3436	2693	743
BOS	3645	2878	767
BRK	3644	2852	792
CHI	3663	2873	790
CHO	3728	2901	827
CLE	3455	2761	694
...	...	...	...

Gruppfiltrering med WHERE

SELECT 
    Team, 
    SUM(DRebound+ORebound) AS TotRebounds,
    SUM(DRebound) AS TotDef,
    SUM(ORebound) AS TotOff
FROM PlayerStats
WHERE ORebound >= 1000
GROUP BY Team;

Använd WHERE för att filtrera enskilda rader och HAVING för numeriskt filter på grupperade rader

Team	TotRebounds	TotDef	TotOff

Utan aggregatfunktion

SELECT 
    Team, 
    SUM(DRebound+ORebound) AS TotRebounds,
    SUM(DRebound) AS TotDef,
    SUM(ORebound) AS TotOff
FROM PlayerStats
GROUP BY Team
HAVING ORebound >= 1000;

Tillämpa HAVING-filtret på en numerisk kolumn med en aggregatfunktion

------------------------------------------------
-- ERROR
Column 'PlayerStats.ORebound' is invalid in the 
HAVING clause because it is not contained in 
either an aggregate function or the GROUP BY 
clause.

Med aggregatfunktion

SELECT 
    Team, 
    SUM(DRebound+ORebound) AS TotRebounds,
    SUM(DRebound) AS TotDef,
    SUM(ORebound) AS TotalOff
FROM PlayerStats
GROUP BY Team
    -- aggregate function SUM()
HAVING SUM(ORebound) >= 1000;

Team	TotRebounds	TotDef	TotOff
OKC	3695	2671	1024

Sammanfattning

Använd inte HAVING för att filtrera enskilda eller ogruppperade rader
Använd WHERE för att filtrera enskilda rader och HAVING för numeriskt filter på grupperade rader
HAVING kan bara tillämpas på en numerisk kolumn i ett aggregatfunktionsfilter

Nu kör vi en övning!

Förbättra frågeprestanda i SQL Server