Question

SELECT
'1' AS SITE
, 'test_id' AS ID
, IFNULL(PREV_DATA, 60) AS PREV_DATA
, IFNULL(PREV_DATA + 2, 60 + 2) AS DATA
FROM 'TABLE'
WHERE ID = 'test_id'
ORDER BY CREATE_DATE DESC
LIMIT 1;

即使没有找到行，我也只想要一行订单非常重要。
我尝试了COUNT（1）或MAX（1），但结果没有按create_date排序...
请帮忙。

-----添加样本数据

+------+---------+-----------+------+---------------------+
| SITE |   ID    | PREV_DATA | DATA |     CREATE_DATE     |
+------+---------+-----------+------+---------------------+
|    1 | test_id |        60 |   62 | 2016-03-21 00:00:00 |
|    1 | test_id |        62 |   64 | 2016-03-21 10:00:00 |
|    1 | test_22 |        60 |   62 | 2016-03-24 00:00:00 |
+------+---------+-----------+------+---------------------+

当ID为'test_id'时，我想要下面的数据。

+------+---------+-----------+------+
| SITE |   ID    | PREV_DATA | DATA |
+------+---------+-----------+------+
|    1 | test_id |        64 |   66 |
+------+---------+-----------+------+

当id为'test33333'时，我想要下面的数据

+------+-----------+-----------+------+
| SITE |   ID      | PREV_DATA | DATA |
+------+-----------+-----------+------+
|    1 | test33333 |        60 |   62 |
+------+-----------+-----------+------+

Answer 1

查看UNION ..所以你选择了一个额外的预定义或＆＃34;空白＆＃34;行但有限制1，它只显示何时找不到另一行

类似的东西（未经测试）：

SELECT
'1' AS SITE
, 'test_id' AS ID
, IFNULL(PREV_DATA, 60) AS PREV_DATA
, IFNULL(PREV_DATA + 2, 60 + 2) AS DATA
, CREATE_DATE
FROM 'TABLE'
WHERE ID = 'test_id'
union 
SELECT
'0' AS SITE
, '' AS ID
, '' AS PREV_DATA
, '' AS DATA
, DATE_SUB(NOW(), INTERVAL -300 YEAR) as CREATE_DATE

ORDER BY CREATE_DATE DESC
LIMIT 1;

如果找不到包含订单的行，mysql会选择一行

1 个答案: