Ah yes, thank you Gerald.
I didn't understand this until now. I guess I should say that 'by design' the linking table will never contain a null, but the left join changes that. Thank you for pointing that out.
gerald_clark wrote:
Brad Tilley wrote:
I should better describe the tables:
computers has 'comp_id' as its primary, unique key.
users has 'user_id' as its primary, unique key.
comp-user-link has two (and only two fields) that are *never* null:
Except within the context of a left join.
Every user in a left join matches up with at least one record in comp-user-link.
If the record is not real, it consists of all NULLs
'comp_id' (which must be unique), and 'user_id'
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