Column with Default value as Sum of TIMESTAMP

I have a table which has 2 columns ( JobDate , RecordTime) -------------------------------------- JobDate | RecordTime | SumCol -------------------------------------- 2019-07-20 | 2019-07-21 | 2019-07-19 | 2019-07-20 | I need SumCol to have a default value as UNIX_TIMESTAMP(JobDate) + UNIX_TIMESTAMP(RecordTime) I've tried creating a virtual column but it gives me this error : **Expression of generated column 'Test2' contains a disallowed function.** that's what I tried: ALTER TABLE jobsTemp ADD SumCol TIMESTAMP AS (UNIx_timestamp(JobDate) + UNIx_timestamp(RecordTime));