"because we have two fields with the same name they make ideal candidates for JOIN"
Maybe it's because it's out of context, but two fields having the same name is not really a good case for using them as a join field. :-) A better case is that both fields are numeric fields with the "parent" table being a unique value. Numeric seeks will always be faster (joining "1234=1234" rather than "rocknbil=rocknbil".)
Sometimes you can name joining field names indicative of what they join
to. For example an message board with users, posts, forums, could have a join table for the user's posts like so:
id userid forumid postid .....
Obviously, the userid will join the user's table on the user record id (or userid) and forumid would join the forum descriptions table on that table's id.
A decent naming convention in anything (table fields, variable names, anything) is such that the field name is somewhat indicative of the field content. Consider
id | a| b| c| d | e
versus
id | user_id | fname | lname | address | city | state
This part is fine as long as you know what's happening
Select tablea.*, tableb.* from tablea, tableb where tablea.ID=tableb.ID
Say table a is users, table b is something related to users, like posts in a message board.
id | userid | fname | lname | email
id | userid | postid | postitle | forumid | postcontent | posted_date
(see below for why I chose "posted_date")
turn to your programming: in PHP (and other languages) there are methods to store a row in an array, so the above example would give you an associative array containing these keys:
id, userid, fname, lname, email,
id, userid, postid, posttitle, forumid, postcontent, posted_date
As you can see there's two keys for id and userid, so requesting
$row['userid']
.. only pulls the first one. In this example the result is identical, they are the same values, but you can see the potential for confusion or incorrect results. As long as you're aware of what happens selecting all with *, it's not a big deal. You can also select specific fields, which is more efficient than * anyway:
Select tablea.username, tableb.posttitle from tablea, tableb where tablea.userid=tableb.userid and tableb.postid=12345
Where field naming can get sticky: field names like this
id first name | last name | datetime
are actually allowed, but you have to back tick them (for two different reasons) to work properly. The names have spaces, and datetime is a mysql reserved word. You should avoid reserved words, but if you must use them, you must make a habit of backticking:
select `first name`, `lastname`, `datetime` from `table` where `id`=1234
So to answer the question, it does matter, but only if you expect someone to understand your code easily in the future.
