MySQL多表SELECT

Question

我对组合 MySQL 查询有点困惑。它是多语言、多目的地网站的一部分，因此我需要从多个表中检索网站的一些文本部分，并进行回退。可能的命中顺序:

corrected@local_tbl > english@local_tbl > corrected@global_tbl > english@global_tbl.

因为它将被高度使用，所以我希望保持快速且连接数较少，但仅返回 1 行。我尝试了以下几种方法，但我确信有更好的解决方案。

<小时/>

FROM 子句中的子查询:如果任何子查询给出 0 行，则子查询终止。即使它有效，也需要一些 php 解释:

SELECT * FROM

(SELECT `sp_content` AS sp_local FROM `loc-ae_siteparts` WHERE `sp_name` = 'name_of_some_sitepart' AND `sp_lang` = 'de' AND `sp_corrected`='1' LIMIT 1) as local,
(SELECT `sp_content` AS sp_local_en FROM `loc-ae_siteparts` WHERE `sp_name` = 'name_of_some_sitepart' AND `sp_lang` = 'en' LIMIT 1) as local_en,
(SELECT `sp_content` AS sp_global, `sp_corrected` as sp_global_corrected FROM `loc-global_siteparts` WHERE `sp_name` = 'name_of_some_sitepart' AND `sp_lang` = 'de' LIMIT 1) as global,
(SELECT `sp_content` AS sp_global_en FROM `loc-global_siteparts` WHERE `sp_name` = 'name_of_some_sitepart' AND `sp_lang` = 'en' LIMIT 1) as global_en

<小时/>

TEMP表:这里我担心性能，不能使用内存引擎，因为它涉及到文本字段。为了小鸟而浪费核武器？

CREATE TEMPORARY TABLE IF NOT EXISTS `random_tbl_name` AS (SELECT `sp_content` FROM `loc-global_siteparts` LIMIT 0);

INSERT INTO `random_tbl_name` SELECT `sp_content` FROM `loc-ae_siteparts` WHERE `sp_name` = 'name_of_some_sitepart' AND `sp_lang` = 'de' AND `sp_corrected` = '1' LIMIT 1;
INSERT INTO `random_tbl_name` SELECT `sp_content` FROM `loc-ae_siteparts` WHERE `sp_name` = 'name_of_some_sitepart' AND `sp_lang` = 'en' LIMIT 1;
INSERT INTO `random_tbl_name` SELECT `sp_content` FROM `loc-global_siteparts` WHERE `sp_name` = 'name_of_some_sitepart' AND `sp_lang` = 'de' AND `sp_corrected` = '1' LIMIT 1;
INSERT INTO `random_tbl_name` SELECT `sp_content` FROM `loc-global_siteparts` WHERE `sp_name` = 'name_of_some_sitepart' AND `sp_lang` = 'en' LIMIT 1;

SELECT * FROM `random_tbl_name` LIMIT 1;

编辑:感谢您的所有回答，它们非常有帮助。

Answer 1

SELECT * FROM
    ((SELECT 1 precedence, `sp_content`
     FROM `loc-ae_siteparts` 
     WHERE `sp_name` = 'name_of_some_sitepart' AND `sp_lang` = 'de' AND `sp_corrected`='1'
     LIMIT 1)
     UNION
     (SELECT 2 precedence, `sp_content` 
     FROM `loc-ae_siteparts` 
     WHERE `sp_name` = 'name_of_some_sitepart' AND `sp_lang` = 'en' 
     LIMIT 1)
     UNION
     ...
    ) x
ORDER BY precedence
LIMIT 1