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我遇到了一个问题，即 mysql 查询卡在“发送数据”状态，有时长达 12-20 分钟，然后我看到其他查询在它后面堆积，直到我用完连接并且网站出现故障. 似乎他们最终会完成，如果我坐下来观看他们足够长的时间，他们会去“删除临时表”，然后他们就会清除。

现在我没有编写这段代码，但我的任务是修复它。我为我们公司做 IT 和服务器管理工​​作，但我将网站的所有实际编码留给我的开发人员。我对 mysql 几乎一无所知，但我的网络人使用的 SELECT 查询对我来说看起来很可疑。如果我没看错，他是在说“在每个表中查找 product_id xxxx 并给我这些结果，然后丢弃其余的”他声称由于表已编入索引，因此以这种方式调用数据不是问题。

如果我从 mysql 控制台运行查询，返回结果需要 3 到 20 秒，而 PHP 实际调用它时显然更长。请注意，它不限于任何一个产品 ID。我要调用的产品似乎没有太大区别。

这是我在 mysql.log 中看到的 

    47384 Connect   ecom_a@localhost on 
    47384 Init DB   ecom_Products
    47384 Query SELECT table_name FROM INFORMATION_SCHEMA.TABLES WHERE table_schema = 'ecom_Products'
    47384 Query 
SELECT * FROM ((SELECT * FROM `AC_Electric_Motor_Run_Capacitors`) 
UNION ALL (SELECT * FROM `AC_Electric_Motor_Start_Capacitors`) 
UNION ALL (SELECT * FROM `AC_Filters`) 
UNION ALL (SELECT * FROM `AC_Gear_Motors`) 
UNION ALL (SELECT * FROM `AC_Line_&_Load_Reactors`) 
UNION ALL (SELECT * FROM `AC_Voltage_Regulators`) 
UNION ALL (SELECT * FROM `Auxiliary_Contact_Blocks`) UNION ALL (SELECT * FROM `Bleed_Down_Resistors`) UNION ALL (SELECT * FROM `Coils`) UNION ALL (SELECT * FROM `Contactors`) UNION ALL (SELECT * FROM `Crimpers`) UNION ALL (SELECT * FROM `DC_Gear_Motors`) UNION ALL (SELECT * FROM `Diesel_Engines`) UNION ALL (SELECT * FROM `Disconnects`) UNION ALL (SELECT * FROM `Electric_Motor_Slide_Bases`) UNION ALL (SELECT * FROM `Electric_Motors`) UNION ALL (SELECT * FROM `Electric_Powered_Water_Pumps`) UNION ALL (SELECT * FROM `Electrical_Enclosures`) UNION ALL (SELECT * FROM `Engine_Powered_Water_Pumps`) UNION ALL (SELECT * FROM `External_Control_Interfaces`) UNION ALL (SELECT * FROM `Float_Switches`) UNION ALL (SELECT * FROM `Foot_Switches`) UNION ALL (SELECT * FROM `Generator_Heads`) UNION ALL (SELECT * FROM `Horizontal_Shaft_Gas_Engines`) UNION ALL (SELECT * FROM `Insulating_Resins`) UNION ALL (SELECT * FROM `Limit_Switches`) UNION ALL (SELECT * FROM `Magnet_Wire`) UNION ALL (SELECT * FROM `Manual_Transfer_Switches`) UNION ALL (SELECT * FROM `Mechanical_Interlock_Blocks`) UNION ALL (SELECT * FROM `Medium_Voltage_Transformers`) UNION ALL (SELECT * FROM `Motor_Starters`) UNION ALL (SELECT * FROM `Multi-fuel_Engines`) UNION ALL (SELECT * FROM `Overload_Relays`) UNION ALL (SELECT * FROM `PTO_Generator_3-Point_Hitch_Mounts`) UNION ALL (SELECT * FROM `PTO_Generator_Drive_Adapters`) UNION ALL (SELECT * FROM `PTO_Generator_Drive_Shafts`) UNION ALL (SELECT * FROM `PTO_Generator_Trailers`) UNION ALL (SELECT * FROM `PTO_Generators`) UNION ALL (SELECT * FROM `Packaged_Standby_Generators`) UNION ALL (SELECT * FROM `Portable_Generator_Covers`) UNION ALL (SELECT * FROM `Portable_Generator_Lifting_Provisions`) UNION ALL (SELECT * FROM `Portable_Generator_Wheel_Kits`) UNION ALL (SELECT * FROM `Portable_Generators`) UNION ALL (SELECT * FROM `Resilient_Vibration_Isolators`) UNION ALL (SELECT * FROM `Resistance_Wire`) UNION ALL (SELECT * FROM `Rotary_Frequency_Converters`) UNION ALL (SELECT * FROM `Rotary_Phase_Converters`) UNION ALL (SELECT * FROM `SO_Cable`) UNION ALL (SELECT * FROM `Single_Phase_Motors_with_Base_Mount`) UNION ALL (SELECT * FROM `Single_Phase_Motors_with_Face_&_Base_Mount`) UNION ALL (SELECT * FROM `Single_Phase_Motors_with_Face_Mount`) UNION ALL (SELECT * FROM `Soft_Starters`) UNION ALL (SELECT * FROM `Special_Metal_Wire`) UNION ALL (SELECT * FROM `Static_Frequency_Converters`) UNION ALL (SELECT * FROM `Static_Phase_Converters`) UNION ALL (SELECT * FROM `Surge_Suppressors`) UNION ALL (SELECT * FROM `Three_Phase_Motors_with_Base_Mount`) UNION ALL (SELECT * FROM `Three_Phase_Motors_with_Face_&_Base_Mount`) UNION ALL (SELECT * FROM `Three_Phase_Motors_with_Face_Mount`) UNION ALL (SELECT * FROM `Transformers_-_General`) UNION ALL (SELECT * FROM `Variable_Frequency_Drives`) UNION ALL (SELECT * FROM `Variable_Transformers`) UNION ALL (SELECT * FROM `Vehicle_&_Equipment_Batteries`) UNION ALL (SELECT * FROM `Vertical_Shaft_Gas_Engines`) UNION ALL (SELECT * FROM `Welding_Cable`) UNION ALL (SELECT * FROM `_Default`)) 
AS t WHERE product_ID = 'LF0009' LIMIT 1
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3 回答 3

3

假设确实需要搜索每个表，最好每个子查询都应用 WHERE 子句。就目前而言，此查询将在所有表上构建一个大型结果集，然后再应用 where 并限制结果集。也许 MySQL 可以优化这一点，也许它不能，但你可以尝试：

....
UNION ALL (SELECT * FROM `AC_Filters` WHERE product_ID = 'LF0009')
UNION ALL (SELECT * FROM `AC_Line_&_Load_Reactors` WHERE product_ID = 'LF0009')
....

我怀疑这个查询是在 PHP 中以编程方式生成的，给定第一个运行的查询，所以做出这个改变应该不难。

更广泛地说，从查询的外观来看，您似乎对每种产品类型都有一个表，而不是一个名为“products”的表，其中包含该类型的 ID 列，以及列出唯一产品的表。

于 2013-05-20T20:43:38.123 回答
2

如果所有这些表的表结构相同，那么它们可能应该是一个带有额外字段以区分的单个表AC_Gear_Motors。AC_Filters看起来所有表都具有相同字段的原因是因为从每个表中选择了所有字段，并且正在联合。

此外，请考虑确定您实际需要哪些字段，而不是使用*.

于 2013-05-20T20:44:24.743 回答
1

这可能会表现得更好......

SELECT only, the, columns, i, actually, need
  FROM one_big_fat_properly_indexed_table t 
 WHERE product_ID = 'LF0009';

...哦，没有 ORDER BY 的 LIMIT 毫无意义，所以我把它关掉了。

于 2013-05-20T21:02:39.737 回答