sql Alter table:基于两列之间的datediff创建列

ALTER TABLE my_table ADD length INT GENERATED ALWAYS AS (DATEDIFF('day', date1, date2))

ALTER TABLE my_table ADD lenght AS int;

UPDATE my_table SET lenght = DateDiff('dd', date1, date2);

-- Don't forget to add a trigger that fires on updated and inserted rows that will keep the value of lenght valid if the date1 or date2 changes