Rails Where Clause PG::SyntaxError: ERROR: subquery must return only one column

I want to take advantage of rails scoping with a custom sql query. You can click this post for I'm trying to do - especially in ActiveAdmin.

How to use a find_by_sql query for an ActiveAdmin index page?

This is my query

LesleyGrade.where('select distinct STC_TERM_GPA, TERM, last, first from lesley_grades order by first, term ASC')

Essentially it's a subquery in a where clause. I only want to return a distinct STC_TERM_GPA for per person per row.

These are my attributes in a lesley_grades table, which might help in understand the information I'm trying to retrieve.

id
user_id
lesley_id
last
first
active
site
cohort
section
sections_title
faculty
completed_term_cred
term
sec_start_date
sec_end_date
grade
stc_cred
active_program
most_recent_program
intent_filed
stc_term_gpa
sta_cum_gpa
start_term
prog_status
last_change_date
created_at
updated_at

So I wanted to see if this would work in Rails C first and this is what I got.

  LesleyGrade Load (51.1ms)  SELECT "lesley_grades".* FROM "lesley_grades"  WHERE (select distinct STC_TERM_GPA,
    TERM,
    last,
    first
    from lesley_grades
order by first, term ASC)
PG::SyntaxError: ERROR:  subquery must return only one column
LINE 1: ...ECT "lesley_grades".* FROM "lesley_grades"  WHERE (select di...
                                                             ^
: SELECT "lesley_grades".* FROM "lesley_grades"  WHERE (select distinct STC_TERM_GPA,
    TERM,
    last,
    first
    from lesley_grades
order by first, term ASC)
=> #<LesleyGrade::ActiveRecord_Relation:0x3fcb44d60944>

I'm not sure how to fix

PG::SyntaxError: ERROR:  subquery must return only one column