如何使用MySQL和Hibernate设置group_concat_max_len

Question

在查询中使用group concat时,由于group concat的默认长度为1024,因此无法获取所有事件组名称,因此如何在现有代码中设置group concat的max_length.

我有一个代码,我在使用group concat并设置max len

==========================================================================
        DATA_QUERY="set group_concat_max_len=10024;
 select group_concat(eg.name) from event_groups eg left join theatres t ON t.theatre_id = eg.theatre_id group by t.theatre_id order by t.application_name"

        Session session = getFacadeLookup().getPersistenceFacade().getHibernateSession();
        Query query = session.createSQLQuery(DATA_QUERY) and execute 

        List<Object[]> lstResult = query.list();
============================================================================

错误集group_concat_max_len不支持此处

Answer 1

尝试设置第group_concat_max_len一个：

session.doWork(connection -> {
    try(Statement statement = connection.createStatement()) {
        statement.execute("SET GLOBAL group_concat_max_len=10024");
    }
});

或Java 8之前的语法：

session.doWork(new Work() {
    @Override
    public void execute(Connection connection) throws SQLException {
        try (Statement statement = connection.createStatement()) {
            statement.execute("SET GLOBAL group_concat_max_len=10024");
        }
    }
});

然后才执行查询：

Query query = session.createSQLQuery(
    "select group_concat(eg.name) " +
    "from event_groups eg " +
    "left join theatres t ON t.theatre_id = eg.theatre_id " +
    "group by t.theatre_id order by t.application_name");
List<Object[]> lstResult = query.list();