根据日期字段更新时间戳列

Question

I've got a table with over 50.000 dates and I need to convert it to a Timestamp field.

Basic table layout:

  Fieldname                Type
+------------------------+-----------+
| calendar_date          | DATE      |
| calendar_unixtimestamp | TIMESTAMP |
+------------------------+-----------+

so basically:

update calender set calendar_unixtimestamp = UNIX_TIMESTAMP(calendar_date)

However, wont work, of course. So I've tried another option which was told me on some goofy website, seems logical. However can't get it to work:

update
  calendar t1
  join calendar t2 on t2.`calendar_date` = t1.`calendar_date`
set
  t1.calendar_unixtimestamp = UNIX_TIMESTAMP(t2.`calendar_date`)
where
  t1.`calendar_date` = t2.`calendar_date`
  

Anyone?

Answer 1

The TIMESTAMP data type is used for values that contain both date and time parts, while UNIX_TIMESTAMP returns an unsigned integer.

You should set calendar_unixtimestamp to INT.

Please see fiddle here .

Answer 2

Benjamin.

I'm not an expert on mysql, but I think you should read this:

http://dev.mysql.com/doc/refman/5.7/en/timestamp-initialization.html

Especially when it says:

By default, the first TIMESTAMP column has both DEFAULT CURRENT_TIMESTAMP and ON UPDATE CURRENT_TIMESTAMP if neither is specified explicitly.

The on UPDATE clause causes the field value to change to the current timestamp whenever the record is updated, so you update it, then it is automatically changed to the current timestamp, the same (or almost) for all the records in your table.

Maybe what you need is a DATETIME column. Timestamp columns are intended to register when a record is created and/or updated. This can be useful for many purposes, including security or conflict resolution when multiple users try to update the same record.

a) If this is what you need, you should first disable the ON UPDATE trigger, then make the update (your first one was OK) and then re-create the trigger(*). Just add a WHERE condition to make sure that you don't try to update nulls. Again, I'm not sure that unix_timestamp is the function you need.

    
    UPDATE calendar
    SET calendar_timestamp = TIMESTAMP(calendar.date) 
    WHERE calendar_date IS NOT NULL

b) If it is not, you simply should change the type of your new column to DATETIME.

(*)Note: Probably it would be easier to drop the column, then create it with the DEFAULT clause but without the ON UPDATE one, or specifying the NULL clause.