使用CAST或STR_TO_DATE链接JSON_EXTRACT失败

Question

我正在尝试从MySQL中的JSONFIELD"数据"中提取日期时间.

但是,如果我执行简单的JSON_EXTRACT,则返回字段类型是JSON.

mysql> select JSON_EXTRACT(data, "$.new_time") from analytics limit 10;
+----------------------------------+
| JSON_EXTRACT(data, "$.new_time") |
+----------------------------------+
| NULL                             |
| "2016-09-30T04:00:00+00:00"      |
| "2016-09-29T05:30:00+00:00"      |
| NULL                             |
| "2016-10-01T05:30:00+00:00"      |
| "2016-09-27T23:00:00+00:00"      |
| NULL                             |
| "2016-09-23T01:30:00+00:00"      |
| "2016-09-23T04:00:00+00:00"      |
| "2016-09-27T01:30:00+00:00"      |
+----------------------------------+

我想将其转换为MySQL DATETIME.但如果我链接JSON_EXTRACT和STR_TO_DATETIME,我会得到所有NULL值:

mysql> select STR_TO_DATE(JSON_EXTRACT(data, "$.new_time") ,"%Y-%m-%d") from analytics_calendaranalytics limit 10;
+-----------------------------------------------------------+
| STR_TO_DATE(JSON_EXTRACT(data, "$.new_time") ,"%Y-%m-%d") |
+-----------------------------------------------------------+
| NULL                                                      |
| NULL                                                      |
| NULL                                                      |
| NULL                                                      |
| NULL                                                      |
| NULL                                                      |
| NULL                                                      |
| NULL                                                      |
| NULL                                                      |
| NULL                                                      |
+-----------------------------------------------------------+

同样,CAST作为DATETIME也会失败:

mysql> select CAST(JSON_EXTRACT(data, "$.new_time") as DATETIME) from analytics_calendaranalytics limit 10;
+----------------------------------------------------+
| CAST(JSON_EXTRACT(data, "$.new_time") as DATETIME) |
+----------------------------------------------------+
| NULL                                               |
| NULL                                               |
| NULL                                               |
| NULL                                               |
| NULL                                               |
| NULL                                               |
| NULL                                               |
| NULL                                               |
| NULL                                               |
| NULL                                               |
+----------------------------------------------------+

当我从字符串值开始时,这两个命令都有效:

mysql> select CAST("2016-09-30T04:00:00+00:00" as DATETIME);
+-----------------------------------------------+
| CAST("2016-09-30T04:00:00+00:00" as DATETIME) |
+-----------------------------------------------+
| 2016-09-30 04:00:00                           |
+-----------------------------------------------+
1 row in set, 1 warning (0.00 sec)

mysql> select STR_TO_DATE("2016-09-30T04:00:00+00:00", "%Y-%m-%d");
+------------------------------------------------------+
| STR_TO_DATE("2016-09-30T04:00:00+00:00", "%Y-%m-%d") |
+------------------------------------------------------+
| 2016-09-30                                           |
+------------------------------------------------------+
1 row in set, 1 warning (0.00 sec)

非常感谢您解决这个问题的任何帮助!

Answer 1

你必须使用JSON_UNQUOTE

select CAST( JSON_UNQUOTE( JSON_EXTRACT(data, "$.new_time")) as DATETIME) from analytics_calendaranalytics limit 10;

会工作.我说是因为你没有提供样本数据.我尝试如下:

select @js := JSON_OBJECT('new_time',"2016-09-30T04:00:00+00:00"  );

select CAST(JSON_UNQUOTE(JSON_EXTRACT(@js,'$.new_time')) as DATETIME);

以下查询也有效

 select STR_TO_DATE(JSON_UNQUOTE(JSON_EXTRACT(@js,'$.new_time')) ,"%Y-%m-%d");