MySql-語法練習2-查詢練習(COUNT、SUM、AVG、MAX、MIN)、新增欄位別名

2021-02-24

COUNT、SUM、AVG、MAX、MIN 用法皆相同

進階練習

數幾筆資料 COUNT(欄位名)

查詢共幾筆資料

SELECT COUNT(stu_pk) FROM grade

加上 where 條件

SELECT COUNT(stu_pk) FROM grade where stu_name='QQQ'

欄位名字可以自己取 AS (別名)

SELECT COUNT(stu_pk) AS myrow FROM grade where stu_name='QQQ'

英文成績的加總

SELECT SUM(stu_english) AS sum_english FROM grade

英文成績的平均

SELECT AVG(stu_english) AS AVG_english FROM grade

英文成績的最高分

SELECT MAX(stu_english) AS MAX_english FROM grade

SELECT stu_name,MAX(stu_english) AS MAX_english FROM grade

英文成績的最低分

SELECT MIN(stu_english) AS MIN_english FROM grade

除了原本的欄位外再增加一個欄位為英文、中文、數學成績的平均

SELECT stu_name,stu_english,stu_chinese,stu_math,(stu_english+stu_chinese+stu_math)/3 as total FROM grade

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