實(shí)訓(xùn)案例名稱：聚合函數(shù)一、任務(wù)介紹MySQL數(shù)據(jù)庫提供了一些常用的聚合函數(shù)。聚合函數(shù)是運(yùn)行在行組上，計(jì)算和返回單個(gè)值的函數(shù)。AVG()函數(shù)用來返回某列的平均值，COUNT()函數(shù)用來返回某列的行數(shù)，MAX()函數(shù)用來返回某列的最大值，MIN()函數(shù)用來返回某列的最小值，SUM()函數(shù)用來返回某列之和。二、實(shí)現(xiàn)步驟1.AVG()函數(shù)#使用用戶名root和相應(yīng)密碼，連接本地MySQLC:\Users\Administrator>mysql-uroot-p123456mysql:[Warning]Usingapasswordonthecommandlineinterfacecanbeinsecure.#使用shop數(shù)據(jù)庫mysql>USEshop;Databasechanged#查詢用戶表user中的數(shù)據(jù)mysql>SELECT*FROMuser;+----+-------+------+------+----------+|id|name|sex

|age

|password

|+----+-------+------+------+----------+|3 |david

|女|28|111111

||4 |小紅

|女|27|123456

||5 |小明

|男|10|123456

||6 |小剛

|男|12|123456

||7 |小王

|男|14|111111

||8 |小綠

|女|34|222222

||9 |曉峰

|男|15|333333

||10 |小影

|女|26|444444

||11 |大梅

|女|27|555555

|+----+-------+------+------+----------+9rowsinset(0.00sec)#計(jì)算平均年齡mysql>SELECTAVG(age)FROMuser;+----------+|avg(age)

|+----------+|21.4444|+----------+1rowinset(0.00sec)mysql>2.COUNT()函數(shù)#使用用戶名root和相應(yīng)密碼，連接本地MySQLC:\Users\Administrator>mysql-uroot-p123456mysql:[Warning]Usingapasswordonthecommandlineinterfacecanbeinsecure.#使用shop數(shù)據(jù)庫mysql>USEshop;Databasechanged#查詢用戶表usermysql>SELECT*FROMuser;+----+-------+------+------+----------+|id|name

|sex

|age

|password

|+----+-------+------+------+----------+|3 |david

|女|28|111111

||4 |小紅

|女|27|123456

||5 |小明

|男|10|123456

||6 |小剛

|男|12|123456

||7 |小王

|男|14|111111

||8 |小綠

|女|34|222222

||9 |曉峰

|男|15|333333

||10 |小影

|女|26|444444

||11 |大梅

|女|27|555555

|+----+-------+------+------+----------+9rowsinset(0.00sec)#計(jì)算年齡大于20的行數(shù)mysql>SELECTCOUNT(*)FROMuserWHEREage>20;+----------+|count(*)|+----------+|5|+----------+1rowinset(0.00sec)mysql>3.MAX()/MIN()函數(shù)#使用用戶名root和相應(yīng)密碼，連接本地MySQLC:\Users\Administrator>mysql-uroot-p123456mysql:[Warning]Usingapasswordonthecommandlineinterfacecanbeinsecure.#使用shop數(shù)據(jù)庫mysql>USEshop;Databasechanged#查詢用戶表usermysql>SELECT*FROMuser;+----+-------+------+------+----------+|id|name

|sex

|age

|password

|+----+-------+------+------+----------+|3 |david

|女|28|111111

||4 |小紅

|女|27|123456

||5 |小明

|男|10|123456

||6 |小剛

|男|12|123456

||7 |小王

|男|14|111111

||8 |小綠

|女|34|222222

||9 |曉峰

|男|15|333333

||10 |小影

|女|26|444444

||11 |大梅

|女|27|555555

|+----+-------+------+------+----------+9rowsinset(0.00sec)#查詢年齡的最大值mysql>SELECTMAX(age)FROMuser;+----------+|MAX(age)|+----------+|34|+----------+1rowinset(0.00sec)#查詢男生年齡的最大值mysql>SELECTMAX(age)FROMuserWHEREsex='男';+----------+|MAX(age)|+----------+|15|+----------+1rowinset(0.00sec)#查詢年齡的最小值mysql>SELECTMIN(age)FROMuser;+----------+|MIN(age)|+----------+|10|+----------+1rowinset(0.00sec)#查詢女生年齡的最小值mysql>SELECTMIN(age)FROMuserWHEREsex='女';+----------+|MIN(age)|+----------+|26|+----------+1rowinset(0.00sec)mysql>4.SUM()函數(shù)#使用用戶名root和相應(yīng)密碼，連接本地MySQLC:\Users\Administrator>mysql-uroot-p123456mysql:[Warning]Usingapasswordonthecommandlineinterfacecanbeinsecure.#使用shop數(shù)據(jù)庫mysql>USEshop;Databasechanged#查詢用戶表usermysql>SELECT*FROMuser;+----+-------+------+------+----------+|id|name

|sex

|age

|password

|+----+-------+------+------+----------+|3 |david

|女|28|111111

||4 |小紅

|女|27|123456

||5 |小明

|男|10|123456

||6 |小剛

|男|12|123456

||7 |小王

|男|14|111111

||8 |小綠

|女|34|222222

||9 |曉峰

|男|15|333333

||10 |小影|女|26|444444

||11 |大梅|女|27|555555

|+----+-------+------+------+----------+9rowsinset(0.00sec)#用戶年齡求和mysql>SELECTSUM(ag