Why does SQLite take such a long time to fetch the data?
- by Derk
I have two possible queries, both giving the result set I want.
Query one takes about 30ms, but 150ms to fetch the data from the database.
SELECT
id
FROM
featurevalues as featval3
WHERE
featval3.feature IN (?,?,?,?)
AND
EXISTS
(
SELECT
1
FROM
product_to_value,
product_to_value as prod2,
features,
featurevalues
WHERE
product_to_value.feature = features.int
AND
product_to_value.value = featurevalues.id
AND
features.id = ?
AND
featurevalues.id IN (?,?)
AND
product_to_value.product = prod2.product
AND
prod2.value = featval3.id
)
Query two takes about 3ms -this is the one I therefore prefer-, but also takes 170ms to fetch the data.
SELECT
(
SELECT
prod2.value
FROM
product_to_value,
product_to_value as prod2,
features,
featurevalues
WHERE
product_to_value.feature = features.int
AND
product_to_value.value = featurevalues.id
AND
features.id = ?
AND
featurevalues.id IN (?,?)
AND
product_to_value.product = prod2.product
AND
prod2.value = featval3.id
) as id
FROM
featurevalues as featval3
WHERE
featval3.feature IN (?,?,?,?)
The 170ms seems to be related to the number of rows from table featval3. After an index is used on featval3.feature IN (?,?,?,?), 151 items "remain" in featval3.
Is there something obvious I am missing regarding the slow fetching? As far as I know everything is properly indexed.. I am confused because the second query only takes a blazing 3ms to run.
