Re: What happens If a table changes during a query/procedure execution

2011/3/9 Vlad Arkhipov <arhipov(at)dc(dot)baikal(dot)ru>:
> 09.03.2011 18:54, Nicolas Barbier:
>>
>> 2011/3/9 Vlad Arkhipov<arhipov(at)dc(dot)baikal(dot)ru>:
>>
>>
>>>
>>> Let there are two transactions that were created with read commited
>>> isolation level. In the first one we're executing a SELECT query:
>>> SELECT * FROM t UNION ALL SELECT * FROM t;
>>>
>>> In the second transaction we're modifying the same table:
>>> INSERT INTO t DEFAULT VALUES;
>>> COMMIT;
>>>
>>> Is it possible that the last UNION part in the first query will retrieve
>>> not
>>> the same rows as the first one?
>>>
>>
>> No, because statements never see changes made by other transactions
>> while they are in flight.
>>
>>
>
> Is it also true if a statement contains subqueries or function calls? For
> instance,
>
> CREATE FUNCTION f() RETURNS NUMERIC AS $$
> BEGIN
>  RETURN (SELECT SUM(a) FROM t);
> END;
> $$ LANGUAGE 'plpgsql';
>
> SELECT a, f() FROM t;
>
> or
>
> SELECT a, (SELECT SUM(a) FROM t) FROM t;

yes, it is same

Regards

Pavel Stehule

>
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