使用子查询、IF和join优化MySQL查询

我有一个复杂的SQL语句，每次调用都需要0.35秒。有50个用户和2周的日历项目，需要245秒，这太长了。我试图优化查询，但目前我还不知道

我对所有相关列都有索引

SELECT 
      DISTINCT tax.ta_id, tax.a_id, ax.status, ax.kunden_id, 
      IF(ax.todo_from != '0000-00-00', DATE_FORMAT(ax.todo_from, '%d.%m'), 'k. day_date') todo_from, 
      IF(ax.todo_until != '0000-00-00', DATE_FORMAT(ax.todo_until, '%d.%m'), 'k. day_date') todo_until, 
      IF((SELECT taj.city FROM suborders taj WHERE taj.a_id = tax.a_id AND taj.order_type = 'BRING' ORDER BY pos_id ASC LIMIT 1) != '', CONCAT(IF((SELECT short_name FROM locations WHERE company_id = '100' AND h_id = tax.h_id) != '', (SELECT short_name FROM locations WHERE company_id = '100' AND h_id = tax.h_id),tax.city),'>', CONCAT((SELECT IF((SELECT short_name FROM locations WHERE company_id = '100' AND h_id = taj.h_id) != '', (SELECT short_name FROM locations WHERE company_id = '100' AND h_id = taj.h_id), taj.city) FROM suborders taj WHERE taj.a_id = tax.a_id AND taj.order_type = 'BRING' AND taj.pos_id >= tax.pos_id ORDER BY pos_id ASC LIMIT 1))), IF((SELECT short_name FROM locations WHERE company_id = '100' AND h_id = tax.h_id) != '', (SELECT short_name FROM locations WHERE company_id = '100' AND h_id = tax.h_id),tax.city)) as city, 
  tax.user_id, tax.day_date, tax.pos_gesamt_id, '4' as class_type 
    FROM 
      suborders tax INNER JOIN orders ax ON (ax.a_id = tax.a_id) 
    WHERE 
      tax.order_type = 'TAKE' AND tax.user_id = '140' AND (tax.day_date = '2013-04-16' AND '2013-04-16' = (SELECT taj.day_date FROM suborders taj WHERE taj.a_id = tax.a_id AND taj.user_id = '140' AND taj.day_date = '2013-04-16' AND taj.user_id = '140' AND taj.order_type = 'BRING' ORDER BY pos_gesamt_id ASC)) AND tax.company_id = '100' GROUP BY tax.ta_id

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也许您可以给我一些建议。

第一次尝试重写（未经测试，因为我不知道您的表格布局）：-

在这一阶段，我不确定我能不能进一步做到这一点，因为这真的让我很困惑事情是如何结合在一起的

问题是，您有很多相关的子查询，而且这些子查询速度很慢（即，子查询依赖于查询外部的字段，因此MySQL必须对每一行执行该子查询）。我已经删除了几个我可以解决的问题，并将它们替换为子查询的连接（使用这些子查询，MySQL可以执行一次子查询，然后将结果连接到主查询）

但是，当您在查询中关联子查询，并且在不同的表和子查询之间重用别名时，会非常混乱

如果我能计算出查询的目的，那么查询的性能将大大提高

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此外，还对主查询使用了GROUPBY，但没有任何聚合列。有时这会代替DISTINCT，但您也有DISTINCT。

您也有组合索引吗？没有，这有什么帮助？这个索引应该包括哪些列？您有很多相关的子查询，这些子查询的性能都可能很差。我正在努力弄清楚你是如何让city字段尝试并重新编码的，如果你解释一下你的查询应该做什么，如果你解释一下表的结构，如果你展示了一个预期结果的示例，你可能会收到更多的答案。目前，您的查询很难理解。

SELECT DISTINCT tax.ta_id, tax.a_id, ax.status, ax.kunden_id, 
      IF(ax.todo_from != '0000-00-00', DATE_FORMAT(ax.todo_from, '%d.%m'), 'k. day_date') todo_from, 
      IF(ax.todo_until != '0000-00-00', DATE_FORMAT(ax.todo_until, '%d.%m'), 'k. day_date') todo_until, 
      IF((SELECT taj.city FROM suborders taj WHERE taj.a_id = tax.a_id AND taj.order_type = 'BRING' ORDER BY pos_id ASC LIMIT 1) != '', 
        CONCAT(
            IF(Sub2.short_name != '', Sub2.short_name,tax.city),
            '>', 
            CONCAT((
                SELECT IF(  Sub3.short_name != '', 
                            Sub3.short_name, 
                            taj.city) 
                FROM suborders taj 
                LEFT OUTER JOIN (SELECT h_id, short_name FROM locations WHERE company_id = '100') Sub3 ON Sub3.h_id = taj.h_id
                WHERE taj.a_id = tax.a_id 
                AND taj.order_type = 'BRING' 
                AND taj.pos_id >= tax.pos_id 
                ORDER BY pos_id 
                ASC LIMIT 1))), 
            IF(Sub2.short_name != '', Sub2.short_name, tax.city)) as city, 
  tax.user_id, tax.day_date, tax.pos_gesamt_id, '4' as class_type 
FROM suborders tax 
INNER JOIN orders ax ON (ax.a_id = tax.a_id) 
INNER JOIN (
    SELECT DISTINCT a_id 
    FROM suborders taj 
    WHERE taj.user_id = '140' 
    AND taj.day_date = '2013-04-16' 
    AND taj.user_id = '140' 
    AND taj.order_type = 'BRING' 
) Sub4 ON Sub4.a_id = tax.a_id 
LEFT OUTER JOIN (SELECT h_id, short_name FROM locations WHERE company_id = '100') Sub2 ON Sub2.h_id = tax.h_id
 WHERE tax.order_type = 'TAKE' 
 AND tax.user_id = '140' 
 AND tax.day_date = '2013-04-16' 
 AND tax.company_id = '100' 
 GROUP BY tax.ta_id