與CAST或STR_TO_DATE鏈接JSON_EXTRACT失敗

Question

我試圖從MySQL中的JSONFIELD「數據」提取日期時間。

但是，如果我做了一個簡單的JSON_EXTRACT，返回字段類型是一個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"  | 
+----------------------------------+ 

我想將其轉換爲MySQL DATETIME。但是，如果我連鎖JSON_EXTRACT和STR_TO_DATETIME，我得到的所有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              | 
+-----------------------------------------------------------+ 

同樣，CAST爲DATETIME也失敗了：當我開始用字符串值

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            | 
+----------------------------------------------------+ 

這兩個命令的工作：

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) 

希望在解決此問題上有任何幫助！

Answer 1

你必須使用JSON_UNQUOTE

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

會工作。我說的是因爲你沒有提供樣本數據。我試過如下：

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

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

下面的查詢也適用

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