Question

我有一个存储过程，我在一段时间间隔内查询数据。所以我写了下面的查询要在存储过程中执行：

SET @quer = CONCAT('INSERT INTO tmp (`time_interval`, `cnt`, `dat`, `txn_id`) (SELECT DATE_FORMAT(\'', tmpStart, '\', \'%H:%i\') as time_interval , COUNT(v.id) as cnt
     , date(v.timestamp) as dat, \"', _txn_id, '\" as txn_id FROM vehicle v WHERE v.timestamp BETWEEN \'', tmpStart, '\'
                        AND \'', tmpEnd, '\' ', _where_clause, ' GROUP BY time_interval)')

但问题是，我希望它在没有值的时间间隔插入0。

Actual : for 01:00 - 02:00 = 12
         for 03:00 - 04:00 = 10
Expected:for 01:00 - 02:00 = 12
         for 02:00 - 03:00 = 0
         for 03:00 - 04:00 = 10

请有人建议我如何更改查询以获得此结果。

感谢。

Answer 1

尝试使用coalesce函数，如果column为null，则coalesce函数将您的值设为默认值，例如：

SELECT id, ..., coalesce(columnWithNulls, DefaultValue) FROM ...

Answer 2

尝试使用IFNULL功能

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Answer 3

我使用此查询得到了答案。使用默认值0联合ALL。

SET @quer = CONCAT('INSERT INTO tmp (`time_interval`, `cnt`, `dat`, `txn_id`) Select * FROM (SELECT DATE_FORMAT(\'', tmpStart, '\', \'%H:%i\') as time_interval , COUNT(v.id) as cnt
 , date(v.timestamp) as dat, \"', _txn_id, '\" as txn_id FROM vehicle v WHERE v.timestamp BETWEEN \'', tmpStart, '\'
                    AND \'', tmpEnd, '\' ', _where_clause, ' GROUP BY time_interval UNION ALL SELECT DATE_FORMAT(\'', tmpStart, '\', \'%H:%i\') as time_interval , 0 as cnt
 , date(\'', tmpStart, '\') as dat, \"', _txn_id, '\" as txn_id) AS A GROUP BY A.time_interval');

如果查询没有数据，请获取默认值？

3 个答案: