Aggregate Operators

• Significant extension of relational algebra.

COUNT (*)

COUNT ( [DISTINCT] A)

SUM ( [DISTINCT] A)

AVG ( [DISTINCT] A)

MAX (A)

MIN (A)

SELECT AVG (S.age)

FROM Sailors S

WHERE S.rating=10

SELECT COUNT (*)

FROM Sailors S

SELECT AVG ( DISTINCT S.age)

FROM Sailors S

WHERE S.rating=10

SELECT S.sname

FROM Sailors S

WHERE S.rating= (SELECT MAX(S2.rating)

FROM Sailors S2)

single column

SELECT COUNT (DISTINCT S.rating)

FROM Sailors S

WHERE S.sname=‘Bob’

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