Simple Inner Join
/*Simple Inner Join action. Joins all rows on both tables as long as there is a match between coluns in both tables.
These are two separate join actions.
Joining the tables grade_levels (gl) and consumer_series (cs) on commonanlity 'consumer_series_id'.
Joining tables models(m) and grade_levels(gl) on commonality 'grade_level_id'.
This part expresses the commonality : on <<aliasTableName1>>.<<commonValue>> = <<aliasTableName2>>.<<commonValue>>
*/
SELECT
distinct gl.grade_level_id, grade_level_name
FROM
consumer_series cs
join grade_levels gl
on cs.consumer_series_id = gl.consumer_series_id
join models m
on m.grade_level_id = gl.grade_level_id
where
cs.display_name = 'tundra'
and m.model_year = cs.current_model_year
and m.active_flag = 1
and m.nonconsumer_flag = 0