小编SQL*_*ter的帖子

我有两个可能的查询,都给出了我想要的结果集.

查询一个大约需要30毫秒,但需要150毫秒才能从数据库中获取数据.

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
    )

查询2需要大约3ms - 这是我更喜欢的那个 - 但是还需要170ms来获取数据.

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 …

我正在使用PHP readfile函数来读取文件并将其打印出来:print readfile ('anyfile').这样可行,但文件的内容长度也会添加到字符串的末尾.为什么？