Assign a value to a field on SELECT statement - mysql

Question

im not sure if im doing well with this field calendar.type_event = NULL. Now works well to me because I need to differentiate the second SELECT as a third type.
I want to do something like calendar.type_event = 'shared_event' to differentiate it. But returns a 0, with NULL returns nothing. This is not the problem only I need to know if I can assign my own value: 'shared_event'.
Thanks a lot
The entire query is:
(SELECT
id, type_event
FROM calendar
WHERE user_id = '.$user_id.'
)
UNION
(SELECT
calendar.id, calendar.type_event = NULL
FROM calendar
RIGHT JOIN avisos ON avisos.app_id = calendar.id
WHERE avisos.user_destiny_id = '.$user_id.'
)
ORDER BY fecha_evento ASC

Answer 1

I need to know if I can assign my own value: 'shared_event'.
Yes, you can. In place of column calendar.type_event just use literal 'shared_event'
Example:
SELECT
calendar.id, 'shared_event'
FROM calendar
RIGHT JOIN avisos ON avisos.app_id = calendar.id
WHERE avisos.user_destiny_id = '.$user_id.'

Answer 2

You should be able to do something like this:
(SELECT
id, type_event
FROM calendar
WHERE user_id = '.$user_id.'
)
UNION
(SELECT
calendar.id, "shared_event"
FROM calendar
RIGHT JOIN avisos ON avisos.app_id = calendar.id
WHERE avisos.user_destiny_id = '.$user_id.'
)
ORDER BY fecha_evento ASC

Answer 3

I think this is what you are looking for:
(SELECT
id, type_event
FROM calendar
WHERE user_id = '.$user_id.'
)
UNION
(SELECT
calendar.id, '' type_event
FROM calendar
RIGHT JOIN avisos ON avisos.app_id = calendar.id
WHERE avisos.user_destiny_id = '.$user_id.'
)
ORDER BY fecha_evento ASC
In the second query, type_event field will contain null values. If the type_event field is a numeric field, you can put 0 (ZERO) instead of '' (empty single quotes/string).