From: | stuart(at)ludwig(dot)ucl(dot)ac(dot)uk (Stuart Rison) |
---|---|
To: | pgsql-sql(at)postgresql(dot)org |
Cc: | stuart(at)ludwig(dot)ucl(dot)ac(dot)uk |
Subject: | [SQL] Tricky -to me!- SQL query. |
Date: | 1999-01-12 11:17:54 |
Message-ID: | v0153050fb2c0d959552d@[128.40.242.176] |
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Lists: | pgsql-sql |
Dear All,
Consider the following table:
dev_brecard=> select * from test order by person;
person|fruit
------+---------
lucy |mandarins
lucy |tomatoes
lucy |pears
lucy |oranges
lucy |apples
peter |pears
peter |apples
peter |oranges
peter |prunes
robert|figs
robert|dates
stuart|apples
stuart|pears
stuart|prunes
stuart|bananas
stuart|kumquats
(16 rows)
(code for creating and populating table is in a PS at the end of this posting)
You can assume that the table is appropriately normalised and that there is
a composite primary key for it (i.e. each COMBINATION of person and fruit
will appear only once and neither of the fields can be NULL)
How do I select from all person who like 'pears' and 'apples' (in this
case, lucy, peter and stuart) or 'pears', 'apples' and 'oranges' (in this
case, lucy and peter)?
I re-read my SQL books but I am still somewhat stumped. Things I could
think of for that sort of query:
1) Select all persons who like 'pears'; Select all persons who like
'apples'; Select all persons who like 'oranges'; Calculate the INTERSECTION
of these sets (this sort of operation appears to use the EXISTS operator?)
2) Use nested subselects:
Select person from test where person in (
Select person from test where fruit='pears' and person in (
Select person from test where fruit='apples' and person in (
Select person from test where fruit='oranges'
)
)
)
What way do you suggest????
Also, am I storing this sort of data in to wrong kind of form (should I
somehow denormalise? if so, how?)?
Could you please cc your answers to: stuart(at)ludwig(dot)ucl(dot)ac(dot)uk
thanks for any help out there!
regards,
Stuart.
PS. Code to cut and paste for table:
create table test (person varchar(25), fruit varchar(25));
insert into test values ('stuart','apples');
insert into test values ('stuart','pears');
insert into test values ('stuart','bananas');
insert into test values ('stuart','kumquats');
insert into test values ('peter','oranges');
insert into test values ('peter','prunes');
insert into test values ('lucy','mandarins');
insert into test values ('lucy','tomatoes');
insert into test values ('peter','apples');
insert into test values ('lucy','apples');
insert into test values ('peter','pears');
insert into test values ('lucy','pears');
insert into test values ('lucy','oranges');
insert into test values ('stuart','prunes');
insert into test values ('robert','figs');
insert into test values ('robert','dates');
+-------------------------+--------------------------------------+
| Stuart Rison | Ludwig Institute for Cancer Research |
+-------------------------+ 91 Riding House Street |
| Tel. (0171) 878 4041 | London, W1P 8BT, UNITED KINGDOM. |
| Fax. (0171) 878 4040 | stuart(at)ludwig(dot)ucl(dot)ac(dot)uk |
+-------------------------+--------------------------------------+
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Next Message | Remigiusz Sokolowski | 1999-01-12 11:44:06 | Re: [SQL] Tricky -to me!- SQL query. |
Previous Message | Dirk Lutzebaeck | 1999-01-12 09:42:57 | Re: [SQL] storing strings with embedded '\' |