Get the reply of an outgoing message in the same row in SQL? - sql

Question

I am trying to get the incoming message for an outgoing message in the same row as response? So, the data looks like below:
user_id message type
1 What's your name? outgoing
1 Nitin incoming
1 What's your age? outgoing
1 17 incoming
2 What's your name? outgoing
2 Aayush incoming
2 What's your age? outgoing
3 What's your name? outgoing
4 What's your name? outgoing
4 Shubham incoming
4 What's your age? outgoing
The output should look like:
user_id message type reply
1 What's your name? outgoing Nitin
1 Nitin incoming
1 What's your age? outgoing 17
1 17 incoming
2 What's your name? outgoing Aayush
2 Aayush incoming
2 What's your age? outgoing No-reply
3 What's your name? outgoing No-reply
4 What's your name? outgoing Shubham
4 Shubham incoming
4 What's your age? outgoing No-reply
The reply is an incoming message for an outgoing message for a user_id & if there is no reply for an outgoing message then the reply column should be filled by 'No-reply'. I have to do this in PSQL. I am currently able to do this in python after fetching data from DB.
Below is my current python code.
df['reply'] = np.where((df['user_id'] == df['user_id'].shift(-1))
& (df['type'].eq('Outgoing') & df['type'].shift(-1).eq('Incoming')),
df['message'].shift(-1), 'No-reply')

Answer 1

Assuming that you have a column that can be used to order the records (called id), you could use lead() as follows:
select
t.*,
case
when type = 'outgoing'
and lead(type) over(partition by user_id order by id) = 'incoming'
then lead(message) over(partition by user_id order by id)
when type = 'outgoing' then 'no reply'
end reply
from mytable
This query checks if the current record has type outgoing and if the next one (for the same user) is of type incoming: if both conditions are true, then it recovers the message on the next record and displays it as reply. If type is outgoing but the next message is not incoming, then it gives no reply. In other cases, nothing is printed.