Question

ok this is hard to explain…

i have the following tables:

table : words
table: word_progress
table: word_set

foreign keys:
words.id = word_set.word_id
word_progress.word_id = words.id
word_progress.user_id = users.id

basically a word is in a word_set. word_progress (it keeps score on a certain word) relates to a user_id and word_id.

the problem is sometimes there is not an entry in word_progress for user_id and word_id. but when it IS there, i wanna be able to use word_progress in the WHERE part of the query. but if it is not there I dont. My work around at the moment is before running the statement, i do an “insert IGNORE IF EXISTS into work_progress (word_id,user_id) values (?,?)” to make sure its there

i have this query

select 
words.* , 
word_progress.progress from words

left join word_progress on word_progress.word_id = words.id
left join word_set on word_set.id = words.word_set_id        

where word_set.id = ?  and word_progress.user_id = ?

but… the problem is sometimes there is no word_progress entry for that word

how can i do this?

Answer 1

you’re already left-joining, so when there’s no data available, you’ll just get null as value for your word_progress-fields. just check for that like this:

...
and
  (
    word_progress.user_id is null
  or
    word_progress.user_id = ?
  )

another way would be to add the user-restriction directly to the join-criteria like this:

...
left join word_progress
  on word_progress.word_id = words.id
  and word_progress.user_id = ?
...

and drop that criteria from the where-part.

note that, in both cases, you’ll have to handle the null-cases for progress later in your code properly.