Re: WG: sql-porting-problem oracle to postgresql with UPDATE/IS NOT NULL

Hello again,

Le 29/07/09 12:21, nha a écrit :
> Hello,
>
> Le 29/07/09 11:48, Gau, Hans-Jürgen a écrit :
>> Sorry, it's a lapse by copying and simplification the original version. that
>> is correct:
>>
>> UPDATE table1 t1
>> SET (t1.id) =
>> (SELECT t3.id FROM table2 t2,table3 t3, table1 t1
>> WHERE t3.field = t2.field
>> AND t2.id = t1.id
>> AND t1.id <> t3.id)
>> WHERE
>> (SELECT t3.id FROM table2 t2,table3 t3, table1 t1
>> WHERE t3.field = t2.field
>> AND t2.id = t1.id
>> AND t1.id <> t3.id) IS NOT NULL;
>> [...]
>> the solution brought by Daryl Richter has no effect.
>
> There is one mistake [...]

To be concrete, a valid version would be:
UPDATE table1 t1
SET id = (something)
WHERE (anotherthing);

> Except this point, the query is valid although I am not sure the result
> is always what you may expect [...]

To "join" table1 column (assumed: id) to the subquery (sub-select here)
expression, table1 recall is not relevant in the subquery. Moreover an
alias "t1" is already defined to table1 (at the beginning of the statement).

A more suitable version would be:
UPDATE table1 t1
SET id = (SELECT t3.id FROM table2 t2, table3 t3
WHERE t3.field = t2.field AND t2.id = t1.id AND t1.id <> t3.id)
WHERE (SELECT t3.id FROM table2 t2, table3 t3
WHERE t3.field = t2.field AND t2.id = t1.id AND t1.id <> t3.id) IS NOT
NULL;

A PostgreSQL-compliant version could also be:
UPDATE table1 t1
SET id = t3.id
FROM table2 t2, table3 t3
WHERE t3.field = t2.field AND t2.id = t1.id AND t1.id <> t3.id AND
t3.id IS NOT NULL;

A PostgreSQL-compliant and faster version may be:
UPDATE table1 t1
SET id = t3.id
FROM table2 t2
INNER JOIN
(SELECT t.id, t.field FROM table3 t WHERE t.id IS NOT NULL) t3
ON t3.field = t2.field
WHERE t2.id = t1.id AND t3.id <> t1.id;

Hoping a satisfying solution is up.

--
nha / Lyon / France.