18 lines
499 B
SQL
18 lines
499 B
SQL
-- #查询男生和女生各多少人
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SELECT sex, COUNT(*)
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FROM t_student
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GROUP BY sex;
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-- # 查询男生和女生分别占总人数的比例
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SELECT sex, COUNT(*) * 100.0 / (SELECT COUNT(*) FROM t_student)
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FROM t_student
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GROUP BY sex;
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-- #查询每门课程下的学生总人数
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SELECT c_name,
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COUNT(DISTINCT stu_cou.s_id) AS sumpeople
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FROM stu_cou
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INNER JOIN t_course on stu_cou.c_id = t_course.c_id
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INNER JOIN t_student on stu_cou.s_id = t_student.s_id
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GROUP BY c_name;
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