Hi listers
mysql> show global variables like "version";
+---------------+--------+
| Variable_name | Value |
+---------------+--------+
| version | 5.1.46 |
+---------------+--------+
1 row in set (0.02 sec)
mysql>
Following problem: Two tables which must be joined differently depending
on the contents of the second table,
the first table esentially contains a date field named datum.
the second table is as follows:
mysql> describe schulung;
+----------+------------------+------+-----+---------+----------------+
| Field | Type | Null | Key | Default | Extra |
+----------+------------------+------+-----+---------+----------------+
| sdat | date | YES | | NULL | |
| tag | text | YES | MUL | NULL | |
| szeit | time | YES | | NULL | |
| speziell | text | YES | | NULL | |
| id | int(10) unsigned | NO | PRI | NULL | auto_increment |
+----------+------------------+------+-----+---------+----------------+
5 rows in set (0.00 sec)
mysql>
Now, if the second table in the sdat field contains a value which is
equivalent to the datum field in the first table (datum = sdat), then
this join must be taken and nothing else.
Otherwise the more general join via the tag field must be taken
(dayname(datum) = tag).
I tried to program this using not exists in the on clause of a join
.... inner join schulung on (if not exists (select sdat from schulung
where sdat = datum) then (datum = sdat)) else dayname(datum) = tag)....
but I got an ERROR 1064 near 'not exists (select sdat ....'
Probably, I have to re-structure the entire statement to an other form
using other constructs? Has anyone had similar problems? How did you
solve it then?
Thank you very much.
suomi
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