I would like to add 7 days to each DATE value. when i add 7 days to the date "2015-11-19" its working and i the new value is "2015-11-26" but when i add it to the "2015-11-26" the date value become "0000-00-00"
this is my query:

```
UPDATE events SET events.event_date = DATE(events.event_date + 7)

```

just for note when i use the next query:

```
UPDATE events SET events.event_date = DATE(events.event_date , interval 7 day)

```

i get those errors:

```
Unrecognized keyword. (near "interval" at position 62)
Unexpected token. (near "7" at position 71)
Unexpected token. (near ")" at position 72)

```