On 2011-02-03 18:07, Bob Price wrote:
I would like to know if there is a way in PostgreSQL to avoid repeating an
expensive computation in a SELECT where the result is needed both as a returned
value and as an expression in the WHERE clause.
I think I've seen it said here that PG avoids redundant multiple
calculations of an expression.
Even so, have you thought about using subqueries?
SELECT id, expensivefunc(value) AS score FROM mytable
WHERE id LIKE '%z%' AND expensivefunc(value)> 0.5;
SELECT id, expensivefunc(value) FROM (
(SELECT id, value FROM mytable WHERE id LIKE '%z%')
) WHERE expensivefunc(value) > 0.5;
or even
SELECT id, score FROM (
SELECT id, expensivefunc(value) AS score FROM (
(SELECT id, value FROM mytable WHERE id LIKE '%z%')
)
) WHERE score > 0.5
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Orhan Kavrakoğlu
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Tart New Media
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