So verwenden Sie die Anweisung „Update in Case' mit Spalten als Aliase
P粉214089349
2023-09-05 17:54:59
<p>Ich habe eine Tabelle namens sales_data mit 3 Spalten (id int, udf varchar(20), date_of_sale datetime).
Ich versuche, den Wochentag der Spalte „date_of_sale“ zu finden, indem ich die Zeit auf 6 Stunden einstelle. Jetzt muss ich die udf-Spalte auf den Wochentag aktualisieren, der date_of_sale entspricht. Ich habe eine Idee für eine Auswahlabfrage, aber wie aktualisiere ich die UDF-Spalte? </p>
<pre class="brush:php;toolbar:false;">selectweekday(subtime(s.date_of_sale ,'6:0:0')) as putdata,
FALL
WHEN Weekday(subtime(s.date_of_sale ,'6:0:0'))=0 THEN 'Sonntag'
WHEN Weekday(subtime(s.date_of_sale ,'6:0:0'))=1 THEN 'Monday'
WHEN Weekday(subtime(s.date_of_sale ,'6:0:0'))=2 THEN 'Tuesday'
WHEN Weekday(subtime(s.date_of_sale ,'6:0:0'))=3 THEN 'Wednesday'
WHEN Weekday(subtime(s.date_of_sale ,'6:0:0'))=4 THEN 'Thursday'
WHEN Weekday(subtime(s.date_of_sale ,'6:0:0'))=5 THEN 'Friday'
WHEN Weekday(subtime(s.date_of_sale ,'6:0:0'))=6 THEN 'Saturday'
ENDE als udf
from sales_data s;</pre></p>
添加生成列（https://dev.mysql.com/doc/refman/8.0/en/create-table- generated-columns.html）以简化处理，并避免数据不一致：
alter table sales_data add weekday varchar(10) GENERATED ALWAYS AS (CASE WHEN weekday(subtime(s.date_of_sale ,'6:0:0'))=0 THEN 'Sunday' WHEN weekday(subtime(s.date_of_sale ,'6:0:0'))=1 THEN 'Monday' WHEN weekday(subtime(s.date_of_sale ,'6:0:0'))=2 THEN 'Tuesday' WHEN weekday(subtime(s.date_of_sale ,'6:0:0'))=3 THEN 'Wednesday' WHEN weekday(subtime(s.date_of_sale ,'6:0:0'))=4 THEN 'Thursday' WHEN weekday(subtime(s.date_of_sale ,'6:0:0'))=5 THEN 'Friday' WHEN weekday(subtime(s.date_of_sale ,'6:0:0'))=6 THEN 'Saturday' END );查看演示：https://dbfiddle.uk/2d5iIvBv
（我没有得到相同的工作日，也许是区域设置？）
您的上述查询已经差不多了。您只需要添加更新语句即可。
下面的查询应该适合您。
update sales_data set udf = case when weekday(subtime(date_of_sale,'6:0:0')) = 0 then 'Sunday' when weekday(subtime(date_of_sale,'6:0:0')) = 1 then 'Monday' when weekday(subtime(date_of_sale,'6:0:0')) = 2 then 'Tuesday' when weekday(subtime(date_of_sale,'6:0:0')) = 3 then 'Wednesday' when weekday(subtime(date_of_sale,'6:0:0')) = 4 then 'Thursday' when weekday(subtime(date_of_sale,'6:0:0')) = 5 then 'Friday' when weekday(subtime(date_of_sale,'6:0:0')) = 6 then 'Saturday' end;