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以下是我拥有的休眠 sql 查询的原始内容：

<sql-query name="countryOfOrigin-limit-country-city-location">
<return alias="rb" class="RecentBooking"/>
    SELECT 
        bb.reserv_num as {rb.reservNum}, 
        bb.origin as {rb.countryOfOrigin}, 
        bb.pick_up_loc as {rb.locationId}, 
        bb.first_date as {rb.bookingDate}, 
        bb.pick_up_time as {rb.pickUpDate}, 
        bb.drop_off_time as {rb.dropOffDate},  
        bb.car_price as {rb.carPrice}, 
        bb.discount as {rb.discount}, 
        bb.exchange_rate as {rb.exchangeRate},
        SUBSTRING(a.internal_class,1,1)as {rb.carClass},
        a.car_type as {rb.carType}, 
        bb.vehicle_type as {rb.vehicleType}, 
        s.name as {rb.supplier}, 
        vv.country as {rb.country}, 
        vv.city as {rb.city}, 
        vv.location as {rb.location}, 
        bb.cur as {rb.currency}, 
        a.pics as {rb.carImage}
    FROM (SELECT * FROM b  WHERE first_date > DATE(NOW()-1)AS bb  
    JOIN a a ON a.id = bb.car_id
    JOIN d  d ON d.id = bb.pick_up_loc
    JOIN supplier s ON s.id = d.supplier_id
    JOIN v_location_trans vv ON vv.location_id = d.location_id
    AND vv.lang=33
    AND vv.country = :country
    AND vv.city = :city
    AND vv.location = :location
    AND bb.origin = :countryOfOrigin
    ORDER BY bb.id DESC
    LIMIT :limit
</sql-query>

sql 运行得足够快，但正如您可能已经注意到的那样，NOW()-1 应该是 NOW() - INTERVAL 1 DAY。

我修改了嵌套的select语句如下：

FROM (SELECT * FROM b WHERE first_date > DATE(NOW() - INTERVAL 1 DAY)) AS bb

该修复程序在结果方面效果很好，但是查询速度大大减慢（几乎几乎瞬间达到几秒钟）。

我相信这是因为 DATE(NOW() - INTERVAL 1 DAY) 被评估了很多次（我们有一个非常大的数据集）。我将如何分离这个计算以便它只发生一次，而不必从 Java 代码（如国家、城市、限制等）中传递它？

我对休眠或 SQL 的经验很少，我尝试在 select 语句之前将计算分离到一个变量中，这是不允许的。我还尝试对 SQL 查询进行小幅更改，但我不断收到运行时错误，可能是由于 SQL 无效。

我该怎么做呢？

谢谢。

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1 回答 1

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bb您正在对整个记录的查询中创建一个新的临时表。

我建议您在创建临时表时过滤掉结果。

例如，如果您在创建临时表时放置 AND 子句

AND bb.origin = :countryOfOrigin

喜欢：

FROM (SELECT * FROM b  WHERE first_date > (NOW() - INTERVAL 1 DAY) AND origin = :countryOfOrigin)AS bb

你也可以限制它。

FROM (SELECT * FROM b  WHERE first_date > (NOW() - INTERVAL 1 DAY) AND origin = :countryOfOrigin LIMIT :limit)AS bb

已编辑——新答案。

我认为您不需要更改INTERVAL 1 DAY，您坚持上一个查询，但将 替换1为86400000等于INTERVAL 1 DAY(24*60*60*1000)

新查询看起来像

FROM (SELECT * FROM b WHERE first_date > (NOW() - 86400000) 
               AND origin = :countryOfOrigin LIMIT :limit) AS bb
于 2012-11-06T10:16:58.857 回答