MySQL creates a student table and queries grades

Create table

CREATE TABLE testdb.users (
  `userid` INT(20) PRIMARY KEY NOT NULL AUTO_INCREMENT,
  `username` VARCHAR(20) NOT NULL,
  `sex` CHAR (3) DEFAULT NULL,
  `age`  INT (3) DEFAULT NULL,
  `num` BIGINT (200) DEFAULT NULL
) ENGINE=INNODB DEFAULT CHARSET=utf8mb4 COLLATE=utf8mb4_0900_ai_ci;

Query table data

1, Query the total score of men and women

SELECT sex, sum(num) FROM testdb.users GROUP BY sex;

2, Query the basic information of each user , Fraction in 90 For excellence ,[80,60) For good , Less than 60 For failing .

select
	userid ,
	username,
	case
		when num >90 then ' good '
		when num <80
		and num>60 then ' good '
		else ' other '
	end as ' achievement '
from
	testdb.users u