Axel Rau wrote:
Am 29.09.2005 um 10:30 schrieb Richard Huxton:
Axel Rau wrote:
SELECT T2.T2_name, COUNT(T1.id) AS xx
FROM T2, T1
WHERE T2.id = T1.fk_t2
GROUP BY T2.T2_name
HAVING COUNT(T1.id) > 1
ORDER BY xx DESC;
t2_name | xx
---------+----
T2-N2 | 3
T2-N3 | 2
(2 rows)
Adding column t1_name to the result set breaks COUNT(T1.id):
SELECT T2.T2_name, T1.T1_name, COUNT(T1.id) AS xx
FROM T2, T1
WHERE T2.id = T1.fk_t2
GROUP BY T2.T2_name, T1.T1_name
HAVING COUNT(T1.id) > 1
ORDER BY xx DESC;
t2_name | t1_name | xx
---------+---------+----
(0 rows)
How can I do this with pg ?
Do what? You don't say what results you are expecting.
Do you want:
1. ALL values of T1_name (in which case what count do you want)?
2. The FIRST value of T1_name (in which case what do you mean by first)?
#1.:
t2_name | t1_name | count
---------+---------+-------
T2-N2 | T1-CCC | 3
T2-N3 | T1-FFF | 2
T2-N2 | T1-BBB | 3
T2-N2 | T1-DDD | 3
T2-N3 | T1-EEE | 2
Ah - this is two questions:
1. What are the unique (t2_name,t1_name) pairings?
2. How many different (t1.id) values are there for each t2.
So - something like:
SELECT names.T2_name, names.T1_name, counts.num_t2
FROM
(
SELECT DISTINCT T2.T2_name, T1.T1_name
FROM T2,T1
WHERE T2.id = T1.fk_t2
) AS names,
(
SELECT T2.T2_name, COUNT(T1.id) AS num_t2
FROM T2, T1
WHERE T2.id = T1.fk_t2
GROUP BY T2.T2_name
HAVING COUNT(T1.id) > 1
) AS counts
WHERE
names.T2_name = counts.T2_name
;
You could write the "names" sub-query with a GROUP BY if you wanted of
course.
--
Richard Huxton
Archonet Ltd
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