Implement dj.U for Universal Sets

[austin-hilberg]

[guzman-raphael]

With the addition of ONLY_FULL_GROUP_BY option to the datajoint/mysql recently, there is increased need and priority for this feature as simple, single-table aggregations (e.g. summation of all values in a column) that were allowed before are no longer properly defined queries.

As an example, previously this would work:

>> University.Student().proj('max(student_id) -> max_id')
ans = 
Object dj.internal.GeneralRelvar
 0:  fakeservices.datajoint.io via TCP/IP   Server version 5.7.33 (encrypted)
    STUDENT_ID    max_id
    __________    ______
    1             3     
3 tuples (0.871 s)

However, it will now (as intended) throw this error on database servers with the new option:

>> University.Student().proj('max(student_id) -> max_id')
ans = 
Object dj.internal.GeneralRelvar
Error using mym
In aggregated query without GROUP BY, expression #1 of SELECT list contains nonaggregated column
'djtest_university.student.student_id'; this is incompatible with sql_mode=only_full_group_by
Error in dj.Connection/query (line 183)
                ret=mym(self.connId, queryStr, v{:});
Error in dj.internal.GeneralRelvar/fetch (line 213)
            ret = self.conn.query(sprintf('SELECT %s FROM %s%s', ...
Error in dj.internal.GeneralRelvar/disp (line 89)
            preview = self.fetch(attrList{:}, sprintf('LIMIT %d', maxRows+1));

The real solution for this will be to structure a query with the new universal set feature once completed. The workaround for now is to simply fetch and perform the aggregation client side until this enhancement is implemented.