2. SQL Basic collation (aggregate function)

Aggregate function--averaging

Select AVG (age) as ages from Xuesheng

Select AVG (Chinese) as language from Xuesheng where class = 1

* Can only operate on numeric types

--Find the number

Select COUNT (*) from xuesheng/* the number of data in the query table */

Select COUNT (*) from Xuesheng where name like ' King% '

Select COUNT (Distinct Class) from Xuesheng

(Two classes)

--Seek maximum value

Select MAX (Chinese) from Xuesheng where class = 1

--To find the minimum value

Select MIN (Chinese) from Xuesheng where class = 1

--Summation

Select SUM (Chinese) from Xuesheng

(You can add distinct to the above function brackets, all by default)

Combined use

Select Avg. As average age, COUNT (*) as number from Xuesheng where class = 1

2. SQL Basic collation (aggregate function)