09.03.2011 18:54, Nicolas Barbier:
2011/3/9 Vlad Arkhipov<arhi...@dc.baikal.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;
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