How to store an ArrayList in MySQL Java?

Question

MySQL

In the course of work, I encountered the problem of saving several key-values ​​in one cell.
For example, a student has a "groups" column in the database, 5-6 id-keys should be written there. How to write values ​​from ArrayList there in Java? Maybe I'm trying to do it wrong. I do this: I take from the ArrayList from the values ​​\u200b\u200bI make the only String, this is with Insert. And at Read on "," I divide into separate lines. How do you implement this, please tell me? Thanks in advance!

Answer 1

You need to create a separate table for groups, which will have 2 columns: student id and group id. Those. the table will have a row for each student group.

Answer 2

If correct, then one field for one object. Usually, several id's are not put into one field. You need 2 tables with fields: student id and group id.

table: student_group
+-------------+-----------+
|  student_id | group_id  |
+-------------+-----------+
|      1      |     4     |
+-------------+-----------+
|      1      |     5     |
+-------------+-----------+
|      1      |     10    |
+-------------+-----------+
|      1      |     99    |
+-------------+-----------+
|      2      |      8    |
+-------------+-----------+
|      2      |     30    |
+-------------+-----------+

Answer 3

You should read about one-to-one, one-to-many, many-to-many database relationships.
If a student can be in several groups, and there can be different students in the group, then this relationship is called many-to-many. In this case, 3 tables are usually created. 1 - students (students), 2 - groups (groups) and 3 is an auxiliary table of two columns - student id and group id (student_group).
for example, a request to select groups in which a student is a member:
To add links, simply add an entry to table 3, for example:
For multiple addition of groups in jdbc there is a batch insert, like this:

String sql = "insert into student_group (student_id, group_id) values (?, ?)";
Connection connection = new getConnection();
PreparedStatement ps = connection.prepareStatement(sql);
String student_id = "Какойто_ид_студента";
ArrayList<String> groups = // это твой лист с группами
 
for (Student group : groups) {
    ps.setString(1, student_id);
    ps.setString(2, group);
    ps.addBatch();
}
ps.executeBatch();
ps.close();
connection.close();