Question

获取错误＆＃34;＃1248 - 每个派生表必须有自己的别名＆＃34;通过phpMyAdmin运行以下查询时：

＆＃13;

SELECT 
    `free_from`, `free_until`
FROM 
(
    SELECT 
        a.end AS `free_from`,
        (SELECT MIN(c.start) FROM bookings c WHERE c.start>a.end) as `free_until`
    FROM bookings a
    WHERE NOT EXISTS (
        SELECT 1
        FROM bookings b
        WHERE b.start BETWEEN a.end AND a.end + INTERVAL 30 Minute
    ) 
    AND a.end BETWEEN '2012-11-16 09:00:00' AND '2012-11-16 22:00:00' 
)

＆＃13;

在这方面你能帮助我吗？

Answer 1

当前的问题是您的外部查询需要别名。但是，对于这种逻辑，您根本不需要子查询。并且，因为MySQL倾向于实现子查询，这可以提高性能：

SELECT a.end AS `free_from`,
       (SELECT MIN(c.start)
        FROM bookings c
        WHERE c.start > a.end
       ) as `free_until`    
FROM bookings a
WHERE NOT EXISTS (SELECT 1
                  FROM bookings b
                  WHERE b.start BETWEEN a.end AND a.end + INTERVAL 30 Minute
                 ) AND
      a.end BETWEEN '2012-11-16 09:00:00' AND '2012-11-16 22:00:00';

mysql - 每个派生表必须有自己的别名

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