如何在codeigniter中显示几个mysql表中的频率计数
如何显示班级学生人数的频率。我在数据库中有几个表。
表=类
+----+---------+---------+
| id | tingkat | nama |
+----+---------+---------+
| 1 | 5 | Kelas 5 |
| 2 | 3 | Kelas 3 |
+----+---------+---------+
表 = 学生
+----+----------+
| id | nama |
+----+----------+
| 1 | 1 |
| 2 | 1 |
| 3 | 1 |
| 4 | 1 |
etc.
表 = student_class
+----+----------+----------+------+
| id | id_kelas | id_siswa | ta |
+----+----------+----------+------+
| 18 | 1 | 18 | 2019 |
| 19 | 1 | 19 | 2019 |
| 20 | 1 | 20 | 2019 |
| 21 | 1 | 21 | 2019 |
| 22 | 1 | 22 | 2019 |
| 23 | 1 | 23 | 2019 |
| 24 | 1 | 24 | 2019 |
| 25 | 1 | 25 | 2019 |
| 26 | 1 | 26 | 2019 |
| 27 | 1 | 27 | 2019 |
| 28 | 1 | 28 | 2019 |
| 29 | 1 | 29 | 2019 |
| 30 | 1 | 30 | 2019 |
| 31 | 1 | 31 | 2019 |
| 1 | 2 | 1 | 2019 |
| 2 | 2 | 2 | 2019 |
| 3 | 2 | 3 | 2019 |
| 4 | 2 | 4 | 2019 |
| 5 | 2 | 5 | 2019 |
| 6 | 2 | 6 | 2019 |
| 7 | 2 | 7 | 2019 |
| 8 | 2 | 8 | 2019 |
| 9 | 2 | 9 | 2019 |
| 10 | 2 | 10 | 2019 |
| 11 | 2 | 11 | 2019 |
| 12 | 2 | 12 | 2019 |
| 13 | 2 | 13 | 2019 |
| 14 | 2 | 14 | 2019 |
| 15 | 2 | 15 | 2019 |
| 16 | 2 | 16 | 2019 |
| 17 | 2 | 17 | 2019 |
+----+----------+----------+------+
GCT10151回答
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四季花海
要计算每个班级的学生人数，您只需要：SELECT id_kelas, COUNT(*) 'count'FROM kelas_siswaGROUP BY id_kelas然后你可以添加额外JOIN的 s 来包含你需要的任何其他内容，比如类元数据。例如：SELECT ks.id_kelas, k.name, COUNT(*) 'count'FROM kelas_siswa ks INNER JOIN kelas k ON ks.id_kelas = k.idGROUP BY ks.id_kelas或者变得花哨：SELECT ks.id_kelas, k.name, COUNT(*) 'count', GROUP_CONCAT(s.nama) 'students'FROM kelas_siswa ks INNER JOIN kelas k ON ks.id_kelas = k.id INNER JOIN siswa s ON ks.id_siswa = s.idGROUP BY ks.id_kelas这还将列出所有学生的姓名以及计数。
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