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Which teachers teach only students in 8th grade?
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Well, that sounds about right.
0:00
Now before you head out for the day,
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there's a few questions about teachers
they're hoping you can help them answer.
0:03
First, the principal wants to do something
nice for the eighth grade teachers.
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If you could get them a list of
which teachers teach eighth grade,
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that would be awesome.
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To figure out which teachers teach
only students in eighth grade,
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let's start by looking
at the teachers table.
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Unfortunately, it doesn't look like
we have any great information here.
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So we're going to have to join out to some
other tables to get that information.
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Looking at the classes table,
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this would be a good table to
join to with our teacher ID.
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And it also gives us access to
the subject ID of the class.
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And in the subjects table,
that's where we have a grade column.
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So, let's start by selecting
everything from the teachers table.
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Then let's JOIN from
here to the CLASSES table
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on TEACHERS.ID = CLASSES.TEACHER_ID.
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And if we run it at this point, we can
see that we've got all the teachers and
1:00
classes, and
we've got this subject ID column.
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Let's use this subject ID column
to join out to the subject table.
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JOIN SUBJECTS ON SUBJECTS.ID
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= CLASSES.SUBJECT_ID.
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And if we run this,
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now we've got the grade information
that we were looking for.
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Last but not least, let's filter
this to only show eighth grade.
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WHERE GRADE, and since there's only one
column in this set that's called grade,
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we don't need to specify
it with any table.
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So WHERE GRADE = 8.
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And here we have all the teachers
that are teaching eight grade.
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However, since we joined through to the
classes table, we're getting one row for
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each class.
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So we're going to need to use
the distinct keyword again.
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Also, we don't need to
return all of this data,
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just the teacher's name
would probably suffice.
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So let's change from selecting everything,
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to just selecting FIRST_NAME,
and LAST_NAME.
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And let's add a DISTINCT on FIRST_NAME.
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And there we go, those are the teachers
that teach eighth grade.
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However, while this does work in this
example, if we had two teachers with
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the same first name,
we'd only be getting one of them here.
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So a better idea is to add
the DISTINCT onto the ID.
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But ID is a column that's in,
well, all of these tables.
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So we need to specify which one.
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Let's use the teachers one.
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And there we go.
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All of the teachers that
teach eighth grade.
2:44
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