mysql - Reuse result of IF condtion in true or false result expression -

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i have following nested query:

select `messages`.*,      if((select `status` messages_status          messages_status.message_id = messages.id , user_id = 149) null,          'unread', messages_status.status) `status` `messages`

what do, if there no messages_status.status set (i.e. if null), should return 'unread'. however, if set, should return value.

currently, returns error: unknown column 'messages_status.status' in 'field list'

do have idea how fix this?

you can't refer result of if's condition in other places. repeat query:

if((select `status` messages_status          messages_status.message_id = messages.id , user_id = 149) null,      'unread',      (select `status` messages_status          messages_status.message_id = messages.id , user_id = 149))     status

but it's clearer use join instead:

select  m.* ,       coalesce(ms.status, 'unknown')    messages m left join         messages_status ms on      ms.message_id = m.id         , ms.user_id = 149

the coalesce function produces first of arguments not null.


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